CHAPTER 5 • The Detailed First Trimester Ultrasound Examination. First Trimester Ultr

 CHAPTER 5 • The Detailed First Trimester Ultrasound Examination

INTRODUCTION

The role of the ultrasound examination in the first trimester has changed over the last 30

years with the introduction of nuchal translucency (NT) screening and with significant

improvements in ultrasound technology. Ultrasound in early gestation, ranging from 6 to

16 weeks, was primarily performed to confirm cardiac activity, location of gestational

sac, pregnancy dating, number of fetuses, and to assess the adnexal regions. In addition,

ultrasound was used to guide invasive procedures such as chorionic villus sampling and

amniocentesis. With the widespread use of the first trimester NT screening, the

assessment of fetal anatomy became part of the early gestation ultrasound and many fetal

malformations that were detected in the second and third trimesters of pregnancy are

now detected in the first trimester. Major fetal anomalies such as fetal hydrops,

anencephaly, body stalk anomaly, large anterior abdominal wall defects, megacystis,

and others (see Table 5.1) are now almost universally detected in the first trimester.1

With accumulating knowledge and expanding expertise, the approach to the first

trimester ultrasound has changed over time. The current goal of the first trimester

ultrasound includes an element of fetal anatomic assessment and in experts’ hands,

detailed evaluation of fetal anatomy is achievable and detection of several major fetal

malformations is now possible with consistency. Advantages of the fetal anatomic

survey in the first trimester include the ability to image the fetus in its entirety in one

view, lack of bone ossification which obstructs view later in gestation, increased fetal

mobility, which allows imaging from many different angles, and the availability of highresolution transvaginal ultrasound, which brings the ultrasound transducer in proximity

to fetal organs. Challenges of the first trimester anatomic survey however include the

need to combine the abdominal and transvaginal approach in some cases, the small size

of fetal organs, and the lack of some sonographic markers of fetal abnormalities that are

commonly seen in the second trimester of pregnancy. In our experience, the performance

of the fetal anatomic survey in the first trimester is enhanced if a systematic approach isemployed.

Table 5.1 • Major Fetal Abnormalities That can Potentially be Easily

Identified on First Trimester Ultrasound

Early hydrops

Anencephaly

Alobar holoprosencephaly

Body stalk anomaly

Ectopia cordis

Large omphalocele

Large gastroschisis

Megacystis

Molar placenta

In this chapter, we report on our systematic approach to the detailed fetal anatomic

survey in the first trimester, defined at 11 to 14 weeks of gestation. We coined the term

detailed to reflect on the comprehensive nature of this approach to fetal anatomy in the

first trimester. This systematic approach is modeled along the “morphology/anatomy”

ultrasound examination in the second trimester. It is important to emphasize that the

performance of the detailed first trimester ultrasound examination requires substantial

operator expertise in obstetric sonography, high-resolution ultrasound equipment, and

knowledge of the current literature on this subject. Optimizing the first trimester

ultrasound examination as described in Chapter 3 of this book, along with the use of the

transvaginal approach with color Doppler and three-dimensional (3D) ultrasound when

clinically indicated, will enhance its accuracy. In Chapter 1, we listed existing national

and international guidelines for the performance of the first trimester ultrasound

examination. The systematic approach that is proposed in this chapter expands on

existing guidelines and is geared toward a detailed evaluation of fetal anatomy in early

gestation. We have developed this approach to the detailed first trimester ultrasound

over several years and have found it to be effective in screening for fetal malformations

in early gestation. Undoubtedly, as new information comes about and with technological

advances in ultrasound imaging, the approach to the detailed first trimester ultrasound

examination will evolve over time.

DETECTION OF FETAL MALFORMATIONS IN THE

FIRST TRIMESTER

Over the past 25 years, several studies reported on the feasibility of ultrasound for thedetection of fetal malformations in early gestation.2–14 Studies on this subject varied

with some reporting high detection rates of fetal anomaly by ultrasound in early

gestation performed in specialized centers with significant expertise.9,12,15–18 Only few

studies reported on the early gestation detection of fetal malformations in large

screening populations with ultrasound examinations performed by several examiners

with various level of expertise.1 Furthermore, the gestational age window varied

between studies, with some reporting detection rates up to 16 weeks of gestation as part

of the “early gestation ultrasound” whereas others have limited the ultrasound

examination to the 11 to 14 weeks of gestation. Of particular interest is the

comprehensive study of Syngelaki et al.,1 which reported on the detection of fetal

anomalies during the 11- to 13-week scan in a population of 44,859 patients after

excluding 332 detected aneuploidies.1 The authors classified the type of first trimester

fetal malformations into four main groups: always detectable, occasionally detectable,

rarely detectable and non-detectable.1 Table 5.2 summarizes the results of this study.1

Table 5.2 • Diagnosis of Fetal Anomalies at 11 to 13 Weeks Scan, after

Excluding Detected Aneuploidies (N = 44,859)

Fetal Abnormality Diagnosis at 11–13 Weeks in Relation to

all Presenta

Neural Tube, Brain, Faceb

Acrania/iniencephaly 29/29 (100%)

Open spina bifida 3/21 (14.3%)

Ventriculomegaly 1/11 (9.1%)

Alobar holoprosencephaly 2/2 (100%)

Facial clefts 1/20 (5%)

Lungs, Heartc

Diaphragmatic hernia 4/8 (50%)

Cardiac anomalies (all) 28/106 (26.4%)

Abdomen, Renald

Omphalocele 60/60 (100%)

Gastroschisis 19/19 (100%)

Megacystis 29/29 (100%)1.

Infantile polycystic kidneys 2/6 (33.3%)

Skeletone

Lethal skeletal dysplasia 3/6 (50%)

Short long bones unilateral 2/4 (50%)

Absent hand/or foot 7/9 (77.8%)

Polydactyly 12/20 (60%)

Others and Multiple

Anomalies

Body stalk anomaly 5/5 (100%)

Cloacal defect 1/1 (100%)

Multiple anomalies 8/8 (100%)

a In cases not diagnosed, absolute number are reported.

b None diagnosed at 11–13 weeks: Hemivertebra (1), microcephaly (1),

craniosynostosis (1), agenesis corpus callosum (10), semilobar

holoprosencephaly (1), cerebellar hypoplasia (1), vermian agenesis (1),

nasopharyngeal teratoma (1), retrognathia (1).

c None diagnosed at 11–13 weeks: Cystic adenomatoid malformation (4),

extralobar sequestration (2), isolated ventricular septal defect (10), cardiac

tumors (4).

d None diagnosed at 11–13 weeks: Bladder exstrophy (1), duodenal

atresia (2), bowel obstruction (1), renal agenesis unilateral (6), renal

agenesis bilateral (1), renal agenesis and multicystic (3), hydronephrosis

unilateral and bilateral (11), multicystic unilateral and bilateral (17), duplex

kidneys (12).

e None diagnosed at 11–13 weeks: Arthrogryposis (1), talipes unilateral

and bilateral (38), ectrodactyly (1).

Modified from Syngelaki A, Chelemen T, Dagklis T, et al. Challenges in the

diagnosis of fetal non-chromosomal abnormalities at 11–13 weeks. Prenat

Diagn. 2011;31:90–102; copyright John Wiley & Sons, Ltd., with

permission.

In our experience, there are four main pathways that result in the prenatal diagnosis

of fetal malformations in the first trimester:

Major Malformation, Clearly Visible: The malformation is easily recognized

during a routine first trimester ultrasound or an ultrasound performed for NT2.

3.

4.

measurement, even with limited skills of the examiner.1,13 Table 5.1 summarizes

some of the major anomalies that are clearly visible in the first trimester.

Thickened Nuchal Translucency: Many fetal malformations have been reported in

association with thickened NT in the presence or absence of chromosomal

aneuploidy. When a thickened NT is encountered, invasive genetic testing is

typically offered along with an ultrasound examination of the fetus. This approach

has led to the first trimester diagnosis of complex cardiac, brain, skeletal,

gastrointestinal, and genitourinary anomalies as presented in various chapters in

this book. On occasions, the associated fetal malformation is not seen in the first

trimester but rather detected in the second trimester or even after birth and the

relationship with an increased NT is thus assumed. Table 9.3 in Chapter 9

summarizes fetal malformations that are known to be associated with thickened NT.

Pregnancies at High Risk for Fetal Malformations: When the pregnancy is at high

risk for fetal anomaly due to a prior history of an affected child or due to a known

inheritance pattern of a specific malformation, a detailed ultrasound in the first

trimester can identify the fetal malformation. Examples include a pregnancy with

prior spina bifida, an autosomal recessive inheritance pattern identified in a prior

pregnancy, or an autosomal dominant inheritance pattern present in one of the

parents. The presence of subtle findings in the first trimester ultrasound can be of

significance in such cases such as the presence of abnormal intracranial

translucency, polydactyly, echogenic kidneys, skeletal abnormalities, and cleft lip

and palate, among others. Several of these subtle findings are discussed in detail in

various chapters in this book.

Detailed First Trimester Ultrasound in Low-Risk Pregnancies: The detection of

fetal malformations in the first trimester can also be the result of a detailed

ultrasound examination that is routinely performed beyond the 11th week of

gestation.11,13,19 With increasing skills and expertise in the detailed first trimester

ultrasound, sonographers and sonologists may decide to apply this approach to all

first trimester pregnancies beyond the 11th week of gestation for fetal anomaly

screening. The detailed first trimester ultrasound will thus be an adjunct to the

second trimester ultrasound examination. It is important to note however that

several limitations currently exist to the detailed first trimester ultrasound

examination and it is thus important to list these limitations before its introduction.

LIMITATIONS OF THE DETAILED FIRST

TRIMESTER ULTRASOUND

Maternal Aspects

One of the main limitations of the detailed first trimester ultrasound examination is

related to the accessibility of the relatively small gestational sac by ultrasound when

maternal body habitus is increased, in the presence of prior abdominal surgery withscarring, and/or in the presence of large leiomyomas with posterior shadowing. In such

conditions, the use of the transvaginal approach or a repeat ultrasound examination at 16

weeks of gestation either with a transabdominal high-resolution linear probe or with the

transvaginal approach, if feasible, may provide sufficient access to assess fetal anatomy

in detail. Occasionally, however, transient maternal contractions may trap the fetus in

one area of the uterus and limit ultrasound accessibility. In our experience, rescanning

the patient 15 to 30 minutes later provides for a better access, because in most cases the

uterine contractions will have resolved (Fig. 5.1).

Indirect Signs of Fetal Malformations

Another limitation of the detailed first trimester ultrasound examination is the absence

of classic, indirect signs of fetal malformations that are commonly seen in the second

trimester. For instance, unlike in the second trimester, bilateral renal agenesis is

commonly associated with normal amniotic fluid volume in early gestation and open

spina bifida does not typically display a lemon or banana sign in the first trimester as is

very often seen in the second trimester of pregnancy. Other examples include the

absence of hyperechogenicity or cystic changes in lung lesions in the first trimester and

the lack of reliance on the abnormal cavum septi pellucidi in several central nervous

system (CNS) lesions as commonly used in the second trimester ultrasound.

Furthermore, fetal biometric changes and growth restriction that are commonly

associated with fetal malformations do not manifest in early gestation and cannot be

used as clues to the presence of associated malformations. It is important to note for all

these reasons and others that the detailed first trimester ultrasound examination for fetal

anatomy survey does not replace the traditional second trimester ultrasound but rather is

complementary to it, especially in a high-risk pregnancy. Pregnant women should be

informed of these limitations.Figure 5.1: A: A transabdominal ultrasound examination in the first trimester

showing a mid-uterine contraction, which is trapping the fetus in the midsection

of the cavity. We were not able to complete the ultrasound examination despite

an attempt by the transvaginal approach. The ultrasound examination was

repeated 35 minutes later (B), which showed resolution of the contraction,

optimization of imaging, and the fetus moving freely within the uterine cavity.

Time in Gestation of Development of Certain Malformations

It is important to note that a major limitation of the detailed first trimester ultrasound

examination for fetal anatomy survey is that some ultrasound findings that are seen in

early gestation may disappear upon follow-up into the second trimester of pregnancy.

Examples include some cases of thickened NT, tricuspid regurgitation, cardiac

ventricular disproportion, early fetal hydrops, and intraabdominal cystic lesions among

others. On the other hand, some malformations that are traditionally visible in the

second trimester, such as cystic lesions of lungs and kidneys, cardiac valvular stenosis,

cortical brain abnormalities, cerebellar vermis dysgenesis, agenesis of corpus

callosum, gastrointestinal atresias, and others are commonly associated with normal

ultrasound findings in early gestation. It is therefore important for the sonographers andsonologists to be familiar with the natural course of congenital malformations and

counsel patients regarding limitations of the first trimester ultrasound examination in that

regard.

Safety Aspects

The detailed first trimester ultrasound examination is performed during a period of

development and rapid growth of fetal organs. It is thus critical to minimize ultrasound

exposure to the fetus, especially the use of pulsed Doppler, given its associated high

energy. As discussed in detail in Chapter 2, the ALARA (as low as reasonably

achievable) principle should always be followed and the operator should ensure that the

thermal and mechanical indices levels always comply with safe practices. The risk of

fetal exposure to ultrasound energy should always be balanced against the benefit of the

ultrasound examination in early gestation. Refer to Chapter 2 of this book for a

comprehensive discussion on ultrasound bioeffects and safety.

THE DETAILED FIRST TRIMESTER ULTRASOUND

In this section, we define our approach to the detailed first trimester ultrasound for fetal

anatomy survey and describe the components of this ultrasound examination. As stated

in the Introduction section of this chapter, the detailed first trimester ultrasound is

performed at 11 to 14 weeks of gestation. Components of the detailed first trimester

ultrasound examination include general overview and fetal biometry, comprehensive

evaluation of fetal anatomy, and an assessment of the uterus and adnexal regions. This

detailed first trimester ultrasound examination is not intended to replace the traditional

second trimester ultrasound but rather to complement it, and in the majority of

pregnancies to provide early reassurance of normalcy. The three components of the

detailed first trimester ultrasound are described in the following sections of this

chapter.

General Overview and Fetal Biometry

Initial aspects of the first trimester ultrasound include the confirmation of the location of

the gestational sac within the endometrial cavity, the presence of cardiac activity, and

the number of fetuses. This can be easily accomplished by the abdominal ultrasound, but

on occasions may require the transvaginal approach. The position of the placenta in

relation to the internal cervical os (Fig. 5.2) should be noted, keeping in mind that most

placenta previas that are diagnosed in early gestation are of no clinical significance and

will resolve upon follow-up ultrasound examination in the third trimester of pregnancy

(see Chapter 15) . In pregnancies with prior cesarean sections, the scar is ideally

assessed by transvaginal ultrasound.20 In these pregnancies the location of the

gestational sac within the endometrial cavity should be noted and implantations in the

lower uterine segment should raise suspicion for increased risk for placenta accreta21,22

(see Chapter 15). Furthermore, implantation of the gestational sac in the cesarean scar

(cesarean scar implantation) is of significant importance given its association withplacenta accreta and serious pregnancy complications.22,23 In the presence of twins or

higher order multiple pregnancy, determining the chorionicity and amnionicity in the

first trimester is of paramount importance. The presence and size of any significant

subchorionic bleed (Fig. 5.3) should also be reported.

Figure 5.2: The position of the placenta (P) should be assessed in relation to

the cervix (arrows) in the first trimester of pregnancy. This is often performed

by the transabdominal ultrasound. Note that the placenta (P) is a previa in this

pregnancy as it is shown to cover the internal cervical os (asterisk). The

presence of placenta previa in the first trimester is of little clinical significance

and should be followed up in the second trimester of pregnancy.Figure 5.3: Subchorionic hematoma (arrows) in a pregnancy at 12 weeks of

gestation in a patient presenting with vaginal bleeding. See text for details.

Biometric measurements for pregnancy dating are an integral part of the first

trimester ultrasound and include the measurement of the crown-rump length, the

biparietal diameter, head circumference, abdominal circumference (AC), and femur

length (FL) (Fig. 5.4). Any significant discrepancy in biometric measurements should

alert for the possible presence of anatomic abnormalities or genetic malformations.

First trimester fetal biometry and pregnancy dating are discussed in detail in Chapter 4.

Table 5.3 lists the components of the general overview and fetal biometry of the

detailed first trimester ultrasound.

Comprehensive Assessment of Fetal Anatomy

The comprehensive assessment of fetal anatomy is an important component of the

detailed first trimester ultrasound. This approach to fetal anatomy in early gestation

involves multiple sagittal, axial, and coronal planes of the fetus. Acquiring the technical

skills required for the display of the corresponding anatomic planes and an in-depth

knowledge of the current literature on this subject are prerequisites for the performance

of the detailed first trimester ultrasound examination. In this section, we present our

systematic approach to the assessment of fetal anatomy in the detailed first trimester

ultrasound examination.

General Anatomic Assessment

The initial step of the fetal anatomy survey in the first trimester involves obtaining an

anterior midsagittal plane of the fetus when technically feasible. This midsagittal plane

allows for a general anatomic assessment, given that the whole fetus is commonlyincluded in this plane (Fig. 5.5). This midsagittal plane displays several important

anatomic landmarks, which are listed in Table 5.4. In this midsagittal plane, the size

and proportions of the fetal head, chest, and body are subjectively assessed and the

following anatomic regions are recognized: fetal facial profile and midline intracranial

structures, the anterior abdominal wall, the fetal stomach, and bladder. By slightly

tilting the transducer from the midline to the left and right parasagittal planes, the arms

and legs can be visualized. Many of the severe fetal malformations that can be detected

in the first trimester (Table 5.1) will show abnormalities in the midsagittal plane and an

in-depth evaluation of fetal anatomic regions, as described in the following sections,

will help to confirm the presence or absence of other fetal abnormalities. When

clinically indicated, color and pulsed Doppler interrogation of the ductus venosus is

also best assessed in this midsagittal plane.Figure 5.4: Fetal biometric measurements in the first trimester include crownrump length (CRL) shown in A, biparietal diameter (BPD) and head

circumference (HC) shown in B, abdominal circumference (AC) shown in C, and

femur length (FL) shown in D.

Table 5.3 • General Overview and Fetal Biometry of the Detailed First

Trimester Ultrasound

Location of gestational sac

Cardiac activity

Number of fetuses

Placental location in relation to cervix

Presence of subchorionic bleed

Fetal biometry

Figure 5.5: Midsagittal plane of the fetus in dorsoposterior position allows for

an evaluation of several key anatomic regions such as the head, face, nuchal

translucency (NT), abdominal wall, and bladder. See Table 5.4 and text form • • •

ore details. CRL, crown-rump length.

Table 5.4 • Midsagittal Plane of the Fetus

Anatomic

Region What to Look for

Head and

facial profile

Forehead to chin with normal physiologic bossing of

forehead. Normal nose, mouth, and intracerebral structures

Head and

body

Normal proportion of head to body with head slightly more

prominent. CRL within the normal range

Thorax Heart activity confirmed. Normal lungs and diaphragm

Abdomen and

pelvis

Normal cord insertion, slightly large abdomen, normal

stomach and bladder, absence of abnormal cystic

structures and echogenic abnormal lesions

CRL, crown-rump length.

The Fetal Head and Neck

Evaluation of the anatomy of the fetal head and neck in the first trimester requires

imaging from the midsagittal, axial, and coronal planes.

Midsagittal Plane

The magnified midsagittal plane of the head and neck enables the assessment of many

anatomic regions to include NT, facial profile with nasal bone and posterior fossa.

Normal anatomic features of the midsagittal plane of the head and neck are shown in

Figure 5.6.

Nuchal Translucency: The quantitative assessment of the NT in the midsagittal plane

of the head and neck is important, as a thickened NT is associated with a large

number of fetal anatomic and genetic abnormalities. The actual measurement of a

thickened NT is also important as the thickness correlates with pregnancy outcome

(see Chapter 9).

Facial Profile: The facial profile is assessed in its entirety to include the forehead,

nasal bridge, nasal bone, maxilla, and mandible (Fig. 5.6). Table 5.5 is a checklist

of the anatomic evaluation of the magnified midsagittal plane of the fetal face in the

first trimester. Abnormalities that can be detected in this plane include anencephaly,

holoprosencephaly, anterior cephalocele, proboscis, absent nasal bone, maxillary

gap or protrusion (associated with cleft palate), epignathus, retrognathia, and others.

Abnormalities that can be detected in the midsagittal plane of the facial profile are

described and illustrated in Chapter 9.

Posterior Fossa: In the midsagittal plane, the anatomy of the posterior fossa can bethoroughly examined (Fig. 5.6) and include the following landmarks: hypoechoic

brainstem with echogenic posterior border, anechoic fourth ventricle, described as

intracranial translucency, posterior echogenic choroid plexus of the fourth ventricle,

and the anechoic cisterna magna, posterior to the fourth ventricle and anterior to the

echogenic occipital bone. Table 5.6 is a checklist of the anatomic evaluation of the

midsagittal plane of the posterior fossa in the first trimester. Abnormalities that can

be detected in this plane include open spina bifida with thickened brainstem and

reduced fluid, increased fluid in the fourth ventricle seen in aneuploidies, Blakes’

pouch cyst, Dandy–Walker malformation, posterior cephaloceles, and other

conditions. Abnormalities that can be detected by the midsagittal plane of the

posterior fossa are presented and illustrated in Chapter 8.

Figure 5.6: Midsagittal plane of the fetal head showing a checklist for the

anatomic regions for a comprehensive assessment of the face and brain. See

Tables 5.5 and 5.6 and text for more details. IT, intracranial translucency.

Table 5.5 • Midsagittal and Coronal Planes of the Fetal Face

Anatomic Region What to Look for

Forehead Normal shape: not too flat, no excessive bossing. No

structure protruding

Nasal region Nose present and nasal bone ossifiedMaxilla No maxillary gap, no protrusion

Mouth Upper and lower lips appear normal

Mandible Normal appearance, no retrognathia

Both eyes In coronal plane, eyes seen with the nose between

Retronasal

triangle In coronal plane, no cleft and normal mandibular gap

Axial Planes

From the midsagittal plane, the transducer is rotated 90 degrees to get the axial planes

of the fetal head, ideally imaged from the lateral aspects. Similar to the approach in the

second trimester, four axial planes of the fetal head in the first trimester allow for a

comprehensive evaluation of CNS anatomy. These planes include the axial plane at the

level of the lateral ventricles, the axial plane at the level of the thalami, the axialoblique plane at the level of the cerebellum and posterior fossa, and the axial plane at

the level of the orbits. Normal anatomic features of these four axial planes of the fetal

head are shown in Figures 5.7, 5.8, and 5.9. Table 5.7 is a checklist of the anatomic

evaluation of the axial planes of the fetal head in the first trimester.

Table 5.6 • Magnified Midsagittal Plane of the Fetal Brain

Anatomic Region What to Look for

Thalamus Visualized as midline structure

Brainstem Visualized with posterior echogenic border, normal

shape, not thickened, not kinked, and not thin

Intracranial

translucency

(Fourth ventricle)

Typical fluid space and echogenic lines, choroid

plexus of fourth ventricle and cisterna magna

visualized

Occipital bone Visualized and intact

The assessment of the normal oval head shape, the continuity of the head contour, the

variable ossification of cranial bones, and the presence of a falx cerebri dividing the

hemispheres into two equal portions can be seen in the first three axial planes (Figs. 5.7

and 5.8). The axial plane at the level of the lateral ventricles (Fig. 5.7, plane 1) shows

two large hyperechoic choroid plexuses that fill significant portions of the lateral

ventricles with a thin peripheral cortex. The choroid plexuses are often asymmetrical

and touch the lateral and medial borders of the ventricles and their area is between 50%

and 75% of the areas of the ventricles (Fig. 5.7, plane 1). The plane at the level of thethalami (Fig. 5.7, plane 2) is used to demonstrate the presence of two separated thalami

and posterior to them the cerebral peduncles with the cerebral aqueduct. The axialoblique plane at the level of the posterior fossa (Fig. 5.8) can be used to visualize the

developing cerebellum and is best shown in transvaginal ultrasound. In this plane, the

hourglass shape of the fourth ventricle and its choroid plexus is best visualized along

with the developing cisterna magna (Fig. 5.8). The fourth plane at the level of the orbits

(Fig. 5.9) demonstrates both eyes with the nose arising between them. Abnormalities

that can be detected by these axial planes of the fetal head include anencephaly,

holoprosencephaly, ventriculomegaly, encephalocele, open spina bifida, and some

severe eyes and face anomalies as described and illustrated in Chapters 8 and 9.

Table 5.7 • Axial Planes (1 to 4) of the Fetal Head in the First Trimester

Anatomic Region What to Look for

Head (planes 1–3) Oval shape, normal contour, and ossification

Biparietal

diameter/head

circumference (plane

2)

Values within the normal range

Falx cerebri (planes

1–3) Visualized, separating two hemispheres

Choroid plexuses of

lateral ventricles

(plane 1)

Two echogenic separated plexuses visualized often

of unequal size and filling more than half of the

lateral ventricles

Thalami (planes 2 and

3)

Two separated thalami visualized, with third

ventricle in between

Cerebral peduncles

(plane 2)

Visualized with aqueduct of Sylvius in between. The

aqueduct is not stuck to the occipital bone

Fourth ventricle (plane

3)

Visualized with choroid plexus of fourth ventricle,

hourglass shape

Eyes (plane 4) In anterior axial planes, two orbits with eyes are

visualized with the nose arising between

Some details are better seen on transvaginal ultrasound.Figure 5.7: Planes 1 and 2 of four axial planes for the anatomic assessment of

the head: Plane 1 corresponds to the transventricular plane and plane 2

corresponds to the transthalamic plane. See Table 5.7 and text for more

details. Planes 1 and 2 are obtained from fetuses at 13 weeks of gestation and

examined by the transabdominal linear probe. See Figures 5.8 and 5.9 for

planes 3 and 4, respectively.Figure 5.8: Plane 3 of four axial planes for the anatomic assessment of the

head: Plane 3 is a slightly oblique plane at the level of the posterior fossa,

demonstrating the developing cerebellum and fourth ventricle as intracranial

translucency (IT). The posterior fossa is easily assessed in the midsagittal view

shown in Figure 5.6. Plane 3 is best assessed by the transvaginal route. See

Table 5.7 and text for more details.Figure 5.9: Plane 4 of four axial planes for the anatomic assessment of the

head: Plane 4 is an axial plane obtained at the level of the orbits demonstrating

two orbits, the eyes, and the nose in between. See text for more details.

Coronal Plane

In an oblique coronal plane of the face, the eyes, orbits, and the retronasal triangle

consisting of the nasal bones, the maxillary processes, and the anterior maxilla with the

alveolar ridge can be recognized (Fig. 5.10) (Table 5.5). The mandibular gap is also

seen in this plane (Fig. 5.10). The coronal plane of the face is helpful in the detection of

severe anomalies of the eyes, large facial clefts, and retrognathia/micrognathia. A more

comprehensive discussion of the normal and abnormal facial anatomy is presented in

Chapter 9.

The Fetal Chest and Heart

The detailed first trimester ultrasound examination of the fetal chest is best performed

by two axial planes and one coronal plane. The two axial planes are most informative

when the fetus is in a dorsoposterior position in the uterus and the coronal plane is

primarily for the assessment of the diaphragm.Figure 5.10: The comprehensive assessment of facial anatomy involves

imaging the face from two planes: the midsagittal plane as shown in Figure 5.6

and the coronal plane shown here. This coronal plane demonstrates both eyes

and the retronasal triangle. See text for more details.

Table 5.8 • Axial Planes (1 and 2) of the Fetal Chest in the First Trimester

Anatomic Region What to Look for

Lungs (plane 1) Both lungs visualized with no pleural effusion

Ribs (plane 1) Ribs visualized, normal shape and length, no

irregularity

Cardiac axis (plane 1) Left cardiac axis around 45 degrees +/− 15-

20 degrees

Four-chamber view (plane 1)

Two almost equal ventricles, two

atrioventricular valves, no pericardial

effusion, antegrade filling of two distinctventricles on color Doppler, no valve

regurgitation

Three-vessel trachea view

(plane 2)

V-shaped aorta and pulmonary artery on

color Doppler with antegrade flow, and

course to the left of trachea

Axial Planes

The two axial planes for the anatomic assessment of the chest and heart include the

plane at the level of the four-chamber view (4CV) and the plane at the level of the threevessel trachea view (3VT). Normal anatomic features of the 4CV and 3VT view are

shown in Figures 5.11 and 5.12 and in Table 5.8.

In the 4CV plane, ribs, lungs, and cardiac position in the chest are assessed, with the

cardiac axis pointing to the left (Fig. 5.11, plane 1). Color Doppler helps to confirm the

presence of two distinct ventricles with separate filling in diastole and the absence of

significant atrioventricular valve regurgitation (Fig. 5.11). When indicated, pulsed

Doppler can assess for the presence or absence of tricuspid valve regurgitation. Color

Doppler at the 4CV also helps in the accurate measurement of the cardiac axis (Fig.

5.11) when an abnormal cardiac axis is suspected. An abnormal cardiac axis or

abnormal cardiac position in the chest is associated with cardiac malformations24 or a

diaphragmatic hernia. Abnormalities that can be detected in this plane include

hypoplastic left or right ventricle, single ventricle, ventricular disproportion, large

septal defects, arrhythmias, pericardial effusion, diaphragmatic hernia, and others.Figure 5.11: The fetal chest is assessed in two planes: axial plane at the level

of the four-chamber view and axial plane at the level of the three-vessel trachea

view. This figure shows plane 1, at the level of the four-chamber view. This

plane is for the anatomic assessment of the heart, lungs, and the rib cage.

Plane 1 is best assessed in gray scale (A) and color Doppler (B) as shown

here. Cardiac axis can also be measured in this plane and adding color Doppler

facilitates its measurement (B). See Table 5.8 and text for more details.Figure 5.12: The fetal chest is assessed in two planes: axial plane at the level

of the four-chamber view (plane 1, shown in Fig. 5.11) and axial plane at the

level of the three-vessel trachea view (plane 2) shown here. Plane 2 is best

obtained in color Doppler showing the pulmonary artery, the aorta, the superior

vena cava, and the trachea. This plane allows for the detection of complex

cardiac anomalies in the first trimester. See Table 5.8, text, and Chapter 11 for

more details.

Given the technical difficulty involved in obtaining the left and right outflow tract

views in the first trimester, we recommend examination of the great vessels in the 3VT

view in color Doppler (Fig. 5.12, plane 2). In the 3VT view, the size of great vessels,

anatomic relationships, and directions of blood flow can be assessed, and the continuity

of the ductal and aortic arches demonstrated (Fig. 5.12, plane 2). The V-shape of the

great vessels with a course left to the echogenic trachea can be recognized (Fig. 5.12,

plane 2). If needed, this plane can also be used to demonstrate the normal or aberrant

course of the right subclavian artery by applying color Doppler at low velocity scale.

Abnormalities that can be detected in the 3VT plane include most conotruncal

anomalies, severe right and left ventricular outflow tract obstructions, right or double

aortic arches, and others. A more comprehensive discussion of the normal and abnormal

cardiac anatomy is presented in Chapter 11.

Coronal Plane

If a diaphragmatic hernia is suspected in the axial plane or has to be ruled out, the lungsand diaphragm are better imaged in a coronal plane slightly anterior to the spine and

ribs (Fig. 5.13). In this plane, the relationship of the stomach, diaphragm, and lungs can

be easily evaluated. A more comprehensive discussion of the normal and abnormal

chest anatomy is presented in Chapter 10.

The Fetal Abdomen and Pelvis

Ultrasound evaluation of the fetal abdomen and pelvis in the first trimester is performed

by three axial planes and one coronal plane. The three axial planes are most informative

when the fetus is in a dorsoposterior position in the uterus.

Axial Planes

The three axial planes are in almost parallel orientation and include the axial plane in

the upper abdomen, the axial plane in the mid-abdomen, and the axial plane in the

pelvis. Normal anatomic features of the three axial planes in the abdomen and pelvis are

shown in Figure 5.14 and in Table 5.9. The upper abdomen plane corresponds to the

AC plane and demonstrates the stomach on the left side and the liver filling the right

abdomen (Fig. 5.14, plane 1). The liver is slightly less echogenic than the lungs in early

gestation. With high resolution, the normal course of the umbilical vein and ductus

venosus, along with the inferior vena cava (IVC), can be demonstrated. The location of

the IVC in the right anterior abdomen is seen compared to the posterior location of the

descending aorta to the left of the spine.

Table 5.9 • Axial Planes (1 to 3) of the Fetal Abdomen and Pelvis in the

First Trimester

Anatomic Region What to Look for

Upper abdomen

(plane 1) Left-sided filled stomach and right-sided liver

Descending aorta and inferior vena cava. Umbilical

vein with ductus venosus.

Middle abdomen

(plane 2)

Normal cord insertion, intact anterior abdominal

wall, and no fluid in abdomen

Lower abdomen and

pelvis (plane 3)

Bladder filled, with length <7 mm. Two umbilical

arteries in color Doppler bordering the bladder

Some details are better seen on transvaginal ultrasound and on color

Doppler.Figure 5.13: Coronal plane of the fetal chest and abdomen for the assessment

of the diaphragm when there is a suspicion of diaphragmatic hernia. This plane

shows both lungs at the same level and the stomach and liver in abdomen. See

text and Chapter 11 for more details.Figure 5.14: Three axial planes (planes 1–3) for the anatomic evaluation of the

fetal abdomen. Plane 1 is at the level of the stomach and demonstrates the

normal position of the stomach and liver. Plane 2 is at the level of the cord

insertion in the abdomen and demonstrates an intact anterior abdominal wall

and plane 3 is in color Doppler at the level of the bladder confirming its

presence along with the presence of two umbilical arteries. See Table 5.9 and

text for more details.

The second plane, the mid-abdomen plane, is obtained at the level of the cord

insertion into the abdomen in order to confirm integrity of the anterior abdominal wall

(Fig. 5.14, plane 2). In this view, the bowels fill the abdomen and are slightly moreechogenic than the liver (Fig. 5.14, plane 2). It is important to note the absence of any

abnormal hyperechoic or anechoic structures in the abdomen and pelvis as this may

suggest the presence of fetal malformations. The kidneys can be occasionally seen in the

posterior abdomen due to their increased echogenicity and due to the anechoic renal

pelvis. It is often difficult however to see the kidneys in the first trimester on the

transabdominal axial plane. Demonstration of the fetal kidneys is best performed in the

coronal plane as discussed later in this section.

The third plane is obtained in the pelvis and demonstrates a normally filled urinary

bladder (Fig. 5.14, plane 3). The length of the filled bladder (obtained in sagittal length)

should be less than 7 mm. Color Doppler is added to this plane to demonstrate the two

umbilical arteries surrounding the bladder (Fig. 5.14, plane 3) and this is performed for

three purposes: (1) to confirm that the anechoic structure is the bladder, especially if the

bladder is mildly filled; (2) to confirm with color Doppler the closed anterior

abdominal wall; and (3) to rule out a single umbilical artery, which can be associated

with other fetal malformations.

Coronal Plane

A coronal oblique plane of the mid-abdomen and pelvis is obtained to demonstrate the

right and left kidneys. This is achieved by turning the transducer 90 degrees from the

axial plane at the level of the mid-abdomen and sliding obliquely to display both

kidneys in the same view (Fig. 5.15). Color Doppler may be added to demonstrate both

renal arteries, thus confirming the presence of both kidneys. This step is not necessary

however, especially when the kidneys are easily demonstrated on gray scale ultrasound.

Abnormalities that can be detected by the axial and coronal planes of the fetal

abdomen and pelvis include abdominal wall defects, abnormal situs, urogenital

anomalies with or without megacystis, intraabdominal cystic structures, bowel dilation,

single umbilical artery, and others. A more comprehensive discussion of the normal and

abnormal fetal abdomen and pelvis is presented in Chapters 12 and 13.

The Fetal Skeletal System

Examination of the fetal skeletal system in the first trimester includes the upper and

lower extremities and the spine. Given the small size of the fetus and the relatively fixed

positions of the extremities in early gestation, we believe that ultrasound evaluation of

the fetal extremities in the first trimester is easier to perform than in the second or third

trimester of pregnancy when fetal crowding obscures visualization. The fetal spine can

also be assessed from various angles and gross abnormalities can be identified.Figure 5.15: When the fetal kidneys are not clearly visualized on axial planes, a

coronal view at the level of the posterior abdomen allows for the best

visualization of the slightly hyperechogenic kidneys.Figure 5.16: The upper extremities in the first trimester can be demonstrated in

an axial view at the level of the face, thorax, or upper abdomen as shown here.

This view shows both arms and hands. Both hands are typically touching in the

first trimester. See Table 5.10 and text for more details.

Axial-Oblique Planes of Fetal Extremities

The approach to the evaluation of the extremities in the first trimester initially involves

two axial-oblique planes: an axial-oblique plane at the level of the chest for the upper

extremities (Fig. 5.16) and an axial-oblique plane at the level of the pelvis for the lower

extremities (Fig. 5.17).

Left and Right Parasagittal Planes of Fetal Extremities

Following the initial approach with the axial-oblique planes and for more detailed

evaluation of the extremities, we recommend tilting the transducer from the midsagittal

plane to left and right parasagittal planes to visualize the left and right arms and legs

respectively (Figs. 5.18 and 5.19). In this approach, with image magnification and with

the use of high-resolution transducers, evaluation of all segments of the extremities can

be performed including upper and lower arms and legs with hands and feet. When

technically feasible we attempt to demonstrate a frontal view of the hands and feet to

visualize the fingers and toes (Figs. 5.20 and 5.21). In our experience, gross anomaliesof the limbs, such as transverse limb defects and other severe deformities, can be

detected in the detailed first trimester ultrasound. The presence of other subtle

abnormalities like polydactyly or clubfeet may escape detection in early gestation.

Table 5.10 is a checklist of the anatomic evaluation of the axial-oblique and

parasagittal planes of the fetal extremities in the first trimester. A more comprehensive

discussion of normal and abnormal extremities is presented in Chapter 14 on the

skeletal system.

Figure 5.17: The lower extremities in the first trimester can be demonstrated in

an axial view at the level of the pelvis as shown here. This view shows both

legs and feet. Both feet are typically touching in the first trimester. See Table

5.10 and text for more details.Figure 5.18: Parasagittal oblique plane demonstrating the three segments of

an upper extremity: upper arm (3), lower arm (2), and hand with fingers (1).

The hands with fingers are often better seen in the first trimester than later on

in gestation.Figure 5.19: Parasagittal oblique plane demonstrating the three segments of a

lower extremity: upper leg (3), lower leg (2), and foot with toes (1). The feet

with toes are often better seen in the first trimester than later on in gestation.Figure 5.20: Once the upper extremity is demonstrated in the parasagittal

oblique plane (Fig. 5.18), the transducer is slightly rotated and the image

magnified to display the hand and fingers as shown here. This approach allows

for the anatomic assessment of the lower arm, hand, and fingers.Figure 5.21: Once the lower extremity is demonstrated in the parasagittal

oblique plane (Fig. 5.19), the transducer is slightly rotated and the image

magnified to display the foot and toes as shown here. This approach allows for

the anatomic assessment of the lower leg, foot, and toes.

Table 5.10 • Axial-Oblique and Parasagittal planes of the Fetal Extremities

in the First Trimester

Anatomic Region What to Look for

Upper limbs Three segments: Humerus, radius, ulna, andhand visualized on both sides

Lower limbs Three segments: Femur, tibia, fibula, and

foot visualized on both sides

Midsagittal, Coronal, and Axial Planes of the Spine

The spine is ideally examined by ultrasound in the first trimester in a midsagittal and

coronal plane, preferably with the fetus in the dorsoanterior position. Where possible

we also attempt to obtain the axial views at the cervical, thoracic, and lumbosacral

regions of the spine (Fig. 14.14), but in our experience, these axial planes are less

informative in the first trimester. The midsagittal view demonstrates the spine in its

entirety (Fig. 5.22) and the coronal view is helpful for the demonstration of spinal

deformities (Fig. 5.23). Table 5.11 is a checklist of the anatomic evaluation of the

sagittal and coronal planes of the fetal spine in the first trimester. Interruption of the

spine, such as in sacral agenesis, is recognized in the midsagittal view, by the short size

of the body of the fetus in comparison with the size of the head. Major spinal defects,

such as body stalk anomaly, are easily recognized in early gestation. More subtle

defects like hemivertebrae, spina bifida, or early sacrococcygeal teratoma are often

difficult to detect when isolated. While open spina bifida can be suspected if the

posterior brain structures appears abnormal and confirmed by the targeted visualization

of the spine with high-resolution transvaginal ultrasound, isolated closed spina bifida

often escape early detection. For more details, refer to Chapter 8 on CNS and Chapter

14 on spinal anomalies.

Three-Dimensional Ultrasound

We encourage the use of 3D ultrasound in surface mode for the display of all four

extremities in one view (Fig. 5.24A) and if the fetus is in a dorsoposterior position, 3D

ultrasound allows for the visualization of the back, in order to demonstrate intact skin

and spine (Fig. 5.24B).25Figure 5.22: Midsagittal view of the fetus in a dorsoposterior position

demonstrating the fetal spine. Note the beginning of ossification of vertebral

bodies and the intact skin covering the back. See Table 5.11 and text for more

details.Figure 5.23: Posterior coronal plane of the fetus demonstrating the spine,

scapula, and ribcage. This plane is helpful when spinal deformities are

suspected. See Table 5.11 and text for more details.

Table 5.11 • Midsagittal and Coronal Planes of the Fetal Spine in the First

Trimester

Anatomic Region What to Look for

Spine, vertebral body

Spine completely seen in one view, no interruption,

no deformities, vertebral bodies ossified after 12

weeks

Ribs, scapulae Ribs visualized, symmetrical, scapulae visualized

Skin over the spine Intact skin covering the spine, no irregular shapeFigure 5.24: Three-dimensional (3D) ultrasound in surface mode in two fetuses

(A and B) in the first trimester. In fetus A, the 3D is obtained from the lateral

aspect and demonstrates both upper and lower extremities. In fetus B, the 3D

ultrasound is obtained from the posterior aspect of the fetus and shows an

intact back. We encourage the use of 3D ultrasound in the first trimester, which

allows for the demonstration of both arms and legs (A) and back (B).

Table 5.12 • Assessment of Uterus and Adnexa

Anatomic Region What to Look for

Uterus Normal shape with absence of Mullerian malformations

and leiomyomas

Adnexae Absence of abnormal adnexal masses

Uterine arteries Doppler interrogation of left and right uterine arteries

when indicated

Assessment of Uterus and Adnexae

Examination of the uterus and adnexal regions is an important part of the detailed first

trimester ultrasound (Table 5.12). The presence, size, and location of any leiomyoma

should be reported (Figs. 5.25 and 5.26). Follow-up ultrasound examinations closer to

term should be considered for leiomyomas in the lower uterine segment in order to

assess for obstruction of the birth canal. The presence of a significant amount ofperitoneal fluid should also be noted. The adnexal regions should be evaluated for the

presence of any abnormal ovarian masses. Often the corpus luteum can still be seen and

enlarged multicystic ovaries can be demonstrated in pregnancies of assisted

reproduction. Evaluation of the adnexa is commonly performed by the transabdominal

approach as the ovaries in the late first trimester are lifted toward the upper pelvis by

the enlarging uterus. The presence of any suspected adnexal masses should be evaluated

by transvaginal ultrasound if feasible as this allows for more detailed assessment.

Adding color Doppler helps to evaluate the vascularity of adnexal masses. Common

adnexal masses in pregnancy include hemorrhagic cysts, endometriomas, dermoid cysts,

and pedunculated leiomyomas (Fig. 5.27). It is important to note that endometriomas can

be decidualized in pregnancy and this appearance may mimic a cancerous tumor (Fig.

5.28). Follow-up ultrasound examination into the second and third trimesters of

pregnancy can help differentiate a decidualized leiomyoma from a malignant tumor. In

patients with Mullerian uterine anomalies, such as bicornuate or septate uterus, the

localization of the pregnancy and the placenta is easier to demonstrate in the first

trimester ultrasound.

Figure 5.26: Large bilobed leiomyoma (arrows) in the fundal region of a

pregnancy at 13 weeks of gestation. The large size of the leiomyoma reduces

the gestational sac. The leiomyoma was too large to be visualized in one image

and panorama view was used.Figure 5.25: Two intramural leiomyomas (arrows) located within the posterior

uterine wall in a pregnancy at 12 weeks of gestation. Location of these

leiomyomas will probably have little impact on the pregnancy. Compare with

Figure 5.26.Figure 5.27: Adnexal masses commonly seen in the first trimester of

pregnancy. Hemorrhagic cyst (A) is shown with characteristic reticular pattern

and fluid level, endometrioma (B) is shown with unilocular ground-glass

appearance, cystic teratoma (C) with echogenic foci from the fat emulsion, and

a pedunculated leiomyoma (D) with solid appearance and minimal vascularity

on color Doppler. Color Doppler shows no vascular signals within the

hemorrhagic cyst and endometrioma.Figure 5.28: Decidualized endometrioma shown in a first trimester pregnancy.

Note the presence of capsular thickening (arrows). Decidualized

endometriomas can be mistaken for a malignant tumor with papillary

projections.

Pregnancy Risk Assessment

Findings from the first trimester ultrasound are currently used in some settings to

provide for pregnancy risk assessment in order to predict pregnancy complications such

as preeclampsia, fetal growth restriction, and preterm delivery. In general, algorithms

combining maternal history, biochemical markers, and first trimester ultrasound

parameters are used to generate individualized pregnancy risk assessment, which

allows for the identification of high-risk pregnancies and for optimization of pregnancy

care. This first trimester risk assessment is incorporated into the concept of “turning the

pyramid of pregnancy care,”26,27 which stratifies pregnancy risk from early gestation

and coordinates prenatal care according to risk.

A main component of the first trimester risk assessment includes Doppler of the

uterine arteries. The uterine arteries are easily identified in the first trimester on a

parasagittal plane of the uterus in color Doppler. The uterine arteries are typically seen

to cross over the hypogastric vessels (Figs. 5.29 and 5.30). The application of uterine

artery pulsed Doppler is considered safe in the first trimester, as the Doppler samplevolume is applied outside of the gestational sac.28,29 Figures 5.29 and 5.30 show the

steps required for the display of the uterine artery for appropriate Doppler sampling.

Details on the use of uterine artery pulsed Doppler along with other first trimester

markers for pregnancy risk assessment are beyond the scope of this book. Interested

readers are advised to refer to the literature on this subject, especially that this

knowledge is advancing rapidly.

Figure 5.29: Steps for obtaining Doppler waveforms of the uterine artery by

the transabdominal route. Step 1: Visualize the cervix in a sagittal view on 2D

ultrasound (arrows). Step 2: Activate color Doppler and tilt the transducer to

left or right in a parasagittal plane until visualizing the left or right uterine artery,

respectively. The uterine artery is seen crossing over the hypogastric vessels.

Step 3: Sample the uterine artery with pulsed Doppler.1.

2.

3.

4.

5.

6.

7.

Figure 5.30: Steps for obtaining Doppler waveforms of the uterine artery by

the transvaginal route. Step 1: Visualize the cervix in a sagittal view on 2D

ultrasound (arrows). Step 2: Activate color Doppler and tilt the transducer to

left or right in a parasagittal plane until visualizing the left or right uterine artery,

respectively. The uterine artery is seen crossing over the hypogastric vessels.

Step 3: Sample the uterine artery with pulsed Doppler. The image is inverted

here from Figure 5.29 as this is the traditional display of gynecologic imaging in

some settings