Chapter 20. Antepartum Fetal Assessment
BS. Nguyễn Hồng Anh
Techniques employed to evaluate fetal health focus on fetal biophysical ndings that include heart rate, movement, breathing,
and amnionic uid production. Antepartum etal surveillance
aims to prevent etal death in pregnancies with complex maternal and etal conditions yet avoid unnecessary interventions
(American College of Obstetricians and Gynecologists, 2021a).
Most etuses will be healthy, and a normal antepartum test
result is highly reassuring. Fetal death within 1 week o a normal test result is rare. Indeed, negative predictive values—true
negative test results for fetal jeopardy—for most of the tests
described are 99.8 percent or higher. In contrast, estimates o
positive predictive values—true positive test results for fetal
jeopardy—are low and range between 10 and 40 percent. e
benet of fetal surveillance is primarily based on circumstantial evidence. No denitive randomized clinical trials have been
conducted or obvious ethical reasons (American College o
Obstetricians and Gynecologists, 2021a).
FETAL MOVEMENTS
■ Fetal Behavioral States
Fetal activity commences as early as 7 weeks’ gestation (Sajapala, 2017; Vindla, 1995). Between 20 and 30 weeks’ gestation, general body movements become organized, and the
etus starts to show rest-activity cycles (Sorokin, 1982). Tese
cycles reect central nervous system development and maturation. By approximately 36 weeks’ gestation, rest-activity cycles
give way to behavioral states in most normal etuses (Peirano,
2003). Four etal behavioral states are described by Nijhuis and
coworkers (1982):
• State 1F is a quiescent state—quiet sleep—with a narrow
oscillatory bandwidth o the etal heart rate.
• State 2F includes frequent gross body movements, continuous eye movements, and wider oscillation o the etal heart
rate. Tis state is analogous to rapid eye movement (REM)
or active sleep in the neonate.
• State 3F includes continuous eye movements in the absence
o body movements and no heart rate accelerations. Tis
state is rare, and its existence is disputed (Pillai, 1990a).
• State 4F is one of vigorous body movement with continuous
eye movements and heart rate accelerations. Tis state corresponds to the awake state in newborns.
At 28 to 30 weeks’ gestation, etuses transition to spend
most of their time in states 1F and 2F, namely, in quiet or
active sleep (Fig. 20-1) (Peirano 2003; Suwanrath, 2010). For
example, at 38 weeks, 75 percent o time is spent in these two
states. Tese behavioral states have been used to develop an
increasingly sophisticated understanding o etal behavior. In
a study o etal urine production, bladder volumes rose during state 1F quiet sleep and signicantly declined during state
2F active sleep due to diminished urine production and inrequent fetal voiding (Oosterhof, 1993). ese phenomena were
thought to represent reduced renal blood ow during active
sleep.
■ Determinants of Fetal Activity
One determinant of fetal activity is the just-described sleepawake cycles, which are independent o maternal ones. In one
study o 16 near-term etuses, the mean duration o a complete
cycle, which included quiet and active states, was 60 minutes. e
mean duration was 23 minutes for the quiet states and 40 minutes
or the active states (imor-ritsch, 1978). Patrick and associates (1982) measured gross etal body movements with real-time
sonography for 24-hour periods in 31 normal near-term pregnancies and ound the longest period o inactivity to be 75 minutes.
Amnionic uid volume is another actor afecting etal activity. Sherer and colleagues (1996) assessed the number o etal
movements in relation to amnionic uid volume in 465 preterm pregnancies during biophysical prole testing. Fetal
activity declined in those with diminished amnionic volumes,
and the authors suggested that a restricted uterine space might
physically limit etal movements.
Patient habits and medications alter etal movement. For
example, maternal smoking decreases etal activity (Coppens,
2001; Taler, 1980). reatment o substance abuse disorders
with methadone and buprenorphine also reduces etal movement
(Jansson, 2017; Wouldes, 2004). Betamethasone administration
is associated with decreased fetal movement for 24 to 72 hours,
and the diurnal pattern is lost (Koenen, 2005; Mulder, 2009).
Te efect is less clear with dexamethasone. Maternal acetaminophen ingestion does not alter etal movement, but a glucose load
does promote activity (Aladjem, 1979; Nitsche, 2015).
■ Maternal Perception
Sadovsky and coworkers (1979b) classied fetal movements as
weak, strong, and rolling according to maternal perceptions
and independent recordings using piezoelectric sensors. As
pregnancy advances, the rate o weak movements drops, and
more vigorous ones rise in frequency. e latter then subside at
term. Presumably, declining amnionic uid volume and space
account or diminished activity at term. Figure 20-2 shows
etal movements during the last hal o gestation in 127 pregnancies with normal outcomes. Te mean number o weekly
movements calculated rom 12-hour daily recording periods
rose rom approximately 200 at 20 weeks’ gestation to a maximum o 575 movements at 32 weeks. Weekly etal movement
counts then declined to an average of 282 at 40 weeks. Another
study o nearly 300 gravidas ound a similar movement pattern
across gestational ages (Bradord, 2019b). More than 90 percent o these women reported stronger movements during the
evening and nighttime.
Women perceive 16 to 45 percent of fetal movements
detected by sonography (Brown, 2016). A higher body mass
index does not decrease maternal perception o etal movement
(Bradord, 2019a; Sasson, 2016). It remains unclear i nulliparity or anterior placental location afect maternal impression o
etal activity (Brown, 2016; Sasson, 2016).
■ Clinical Application
Because women may perceive a decline in etal movement in
the days to weeks preceding stillbirth, maternal perception o
etal movement has been evaluated as a preventive aid (Heazell,
2008; Stacey, 2011). However, the optimal etal-movement
protocol remains undened (Mangesi, 2015). Some methods
rely on quantitative counts, such as 10 movements in 2 hours,
whereas others rely on a mother's subjective impression. In one
study, more than 68,000 pregnancies were randomly assigned
between 28 and 32 weeks’ gestation to an objective or subjective assessment group (Grant, 1989). Women in the objective
arm were instructed to record the time needed to eel 10 movements each day. is required an average of 2.7 hours daily.
Women in the subjective group were inormally asked about
movements during prenatal visits. Reports o decreased etal
motion were then evaluated with tests o etal well-being. Antepartum death rates or normal singleton etuses were similar
in the two study groups, and most stillborn etuses were dead
by the time the mothers reported or medical attention. Rather
than concluding that maternal perceptions were meaningless,
the authors concluded that inormal maternal impressions were
as valid as ormally recorded etal movement counts.
Women's knowledge o these protocols also vary. In one
survey of more than 400 gravidas, 85 percent noted receiving
30–31 32–33 34–35 36–37 38–40
100
0
Gestational age (wks)
20
40
60
Number of sleep minutes
Number of accelerations
80
100
0
20
40
60
80
Active sleep
Active sleep acceleration
Quiet sleep acceleration
Quiet sleep
FIGURE 20-1 The change in fetal sleep patterns (blue columns)
and corresponding number of accelerations (graph lines). As the
third trimester advances, fetuses spend more time in active sleep
and the number of accelerations per hour increases.
18
Gestational age (weeks)
Fetal movements
(weekly average)
600
500
400
300
200
100
0
20 22 24 26 28 30 32 34 36 38 40
FIGURE 20-2 Graph depicts averages of fetal movements
counted during 12-hour periods (mean ± SEM). (Data from
Sadovsky, 1979a.)Antepartum Fetal Assessment 385
CHAPTER 20
instruction rom their provider regarding normal etal movement (Pollock, 2019). However, 60 percent described it as a
subjective assessment, and 40 percent reported a quantitative
method. In another study, more than two thirds o women
could not explain fetal movement monitoring techniques
(Berndl, 2013).
Although a long-standing pillar o maternal care, etal movement surveillance may not be as predictive as thought. Nearly
6 to 7 percent o pregnancies are complicated by decreased
etal movement, but stillbirth rates are not increased in these
cases (Harrington, 1998; Scala, 2015). In one study o more
than 400,000 pregnancies complicated by decreased fetal
movement, directed patient and staf education coupled with
a prescriptive management plan did not reduce the stillbirth
incidence (Norman, 2018). Aside rom stillbirth, some data
show that decreased etal movement may help identiy growthrestricted etuses beore birth (Saastad, 2011; Scala, 2015). In
one o these studies, nearly 1100 pregnancies were assigned to
subjective or objective assessment o etal activity. Te rate o
1-minute Apgar scores ≤3 was signicantly reduced (0.4 versus
2.3 percent) when counting was used (Saastad, 2011).
Tus, although most pregnancies complicated by decreased
etal movement will result in normal outcomes, maternal perception o reduced etal activity warrants urther evaluation.
No consensus guides a provider's response. Care is individualized and inuenced by gestational age and pregnancy comorbidities. In low-risk pregnancies, documenting etal heart tones
and adequate amnionic uid volume may be sucient. For
older etuses, tests described in the upcoming sections are typically added. Our practice is a nonstress test and sonographic
measurement o amnionic uid volume.
Many women report excessive etal movement in the third
trimester. Its risk, i any, is poorly understood. Stacey and colleagues (2011) reported that a single episode o vigorous etal
activity is associated with a greater risk or etal death. Similarly,
others have described maternal perception o a single episode
o excessive o etal movement in the weeks prior to a stillbirth
diagnosis (Heazell, 2017; Whitehead, 2020). More research is
needed prior to recommending intervention.
FETAL BREATHING
Small inward and outward ow o tracheal uid, indicating
thoracic movement, was rst identied in fetal sheep (Dawes,
1972). Tese chest wall movements difer rom those ollowing birth in that they are discontinuous. Another eature o
etal respiration is paradoxical chest wall movement (Fig. 20-3)
( Johnson, 1988). In the newborn or adult, the opposite occurs.
One interpretation of paradoxical respiratory motion might
be coughing to clear amnionic uid debris. Although the
physiological basis or the breathing reex is not completely
understood, such exchange o amnionic uid appears to be
essential for normal lung development (Chap. 7, p. 130). Dawes
(1974) identied two types of respiratory movements. e rst
are gasps or sighs, which occurred at a frequency of 1 to 4 per
minute. Te second, irregular bursts o breathing, occurred at
rates up to 240 cycles per minute. ese latter rapid respiratory
movements were associated with rapid eye movement. Badalian
and associates (1993) studied the maturation o normal etal
breathing using color ow and spectral Doppler analysis of
nasal uid ow as an index o lung unction. Tey suggested
that etal respiratory rate declined in conjunction with increasing respiratory volume at 33 to 36 weeks’ gestation and coincided with lung maturation.
Many investigators have used sonography to determine
whether chest wall movements might reect etal health. Several
variables in addition to hypoxia afect these movements. Tese
include maternal hypoglycemia, sound stimuli, cigarette smoking, amniocentesis, impending preterm labor, gestational age,
fetal heart rate, and labor—during which it is normal for fetal
respiration to cease.
Because etal breathing movements are episodic, interpretation o etal health when respirations are absent may be di-
cult. Patrick and coworkers (1980) performed continuous
24-hour observation using sonography to characterize fetal
breathing patterns during the last 10 weeks o pregnancy. A
total of 1224 hours of fetal observation in 51 pregnancies were
collected. Figure 20-4 displays the percentages o time spent
breathing near term. Substantively diminished breathing during the night suggests a diurnal pattern. In addition, breathing
activity is enhanced somewhat ollowing maternal meals. otal
absence o breathing was observed in some o these normal
etuses or up to 122 minutes, indicating that etal evaluation
to diagnose absent respiratory motion may require long periods
o observation.
Te potential or breathing activity to be an important sole
marker of fetal health is unfullled because of the multiple
Expiration
B Expiration
Fetal
chest
Fetal
abdomen
A
Inspiration
Fetal
chest
Fetal
abdomen
FIGURE 20-3 Paradoxical chest movement with fetal respiration.
During inspiration (A), the chest wall paradoxically collapses and
the abdomen protrudes, whereas during expiration (B), the chest
wall expands.386 The Fetal Patient
Section 6
actors that afect breathing. Most clinical applications couple
etal breathing with other biophysical indices. For example,
fetal breathing is one component of the biophysical prole
(p. 389).
CONTRACTION STRESS TEST
During a uterine contraction, pressures generated by the myometrium exceed the collapsing pressure o the vessels coursing
through it. Tis ultimately lowers blood ow to the placenta's
intervillous space. Brie periods o impaired oxygen exchange
result. I uteroplacental pathology is present, oxygen exchange
to the etus is urther diminished, and late etal heart rate decelerations appear (Chap. 24, p. 452). ese downward- sloping
heart-rate waveorms begin with the onset o the uterine
contraction waveorm or just beyond its acme. Instead, contractions may produce variable decelerations as a result o cord
compression. Tis suggests oligohydramnios, which is oten
comorbid with placental insuciency.
Ray and associates (1972) used this concept in 66 complicated pregnancies and developed the oxytocin challenge test,
which was later called the contraction stress test (CST). A positive test result, that is, an abnormal result, is uniorm repetitive
late etal heart rate decelerations. In their study, the tests were
repeated weekly, and the authors concluded that negative CS
results, that is, normal results, orecasted etal health.
o perorm the test, contractions are induced with either
intravenous oxytocin or nipple stimulation. I at least three
spontaneous contractions of 40 seconds or longer are present in a 10-minute span, no uterine stimulation is necessary
(American College of Obstetricians and Gynecologists, 2021a).
Te etal heart rate and uterine contractions are recorded simultaneously by external monitors. With oxytocin, a dilute intravenous inusion is used to establish a satisactory contraction
pattern (Freeman, 1975). At Parkland Hospital, 20 units o
oxytocin are mixed in 1 liter o Ringer solution and initiated at
a rate o 6 mU/min. Te rate is increased by 6 mU/min every
40 minutes to achieve the just-discussed contraction pattern.
Nipple stimulation to induce uterine contractions or a CS
is usually successful (Huddleston, 1984). One method involves
a woman rubbing one nipple through her clothing or 2 minutes or until a contraction begins. Tis 2-minute nipple stimulation ideally will induce a pattern o three contractions per
10 minutes. I not, ater a 5-minute rest interval, she is instructed
to retry nipple stimulation to achieve the desired pattern. I this
is unsuccessul, dilute oxytocin may be used.
CS results are interpreted according to the criteria shown
in Table 20-1. Disadvantageously, the average CST requires
90 minutes to complete. Compared with oxytocin, nipple stimulation shortens testing time and costs less. During a CST, some
have reported unpredictable uterine hyperstimulation and etal
distress, whereas others did not nd excessive activity to be harmful
(Frager, 1987; Schellpefer, 1985). Relative contraindications to a
CS include those conditions that contraindicate vaginal delivery.
NONSTRESS TEST
Te nonstress test (NST) also is used to assess etal well-being
and employs the phenomenon o etal heart rate acceleration
in response to etal movement (Freeman, 1975; Lee, 1975).
During an NST, these accelerations are correlated with fetal
movements perceived by the mother.
Compared with a CS, an NS is easier to perorm, and normal results can be used to further dene false-positive CST results.
Simplistically, the NS is primarily a test o etal condition, and it
difers rom the CS, which is considered a test o uteroplacental
unction. Currently, NS is the most widely used primary testing
method or assessment o etal well-being. It has also been incorporated into the biophysical prole, discussed later (p. 389).
TABLE 20-1. Criteria for Interpretation of the Contraction Stress Test
Negative: no late or significant variable decelerations
Positive: late decelerations following 50% or more of contractions (even if the contraction frequency is fewer than three in
10 minutes)
Equivocal-suspicious: intermittent late decelerations or significant variable decelerations
Equivocal-hyperstimulatory: fetal heart rate decelerations that occur in the presence of contractions more frequent than
every 2 minutes or lasting longer than 90 seconds
Unsatisfactory: fewer than three contractions in 10 minutes or an uninterpretable tracing
50
40
30
20
10
8 am Noon 4 pm 8 pm Midnight
4 am 8 am
Time spent breathing (percent)
Time of day
FIGURE 20-4 The percentage of time spent breathing by 11
fetuses at 38 to 39 weeks’ gestation. Fetal breathing activity
significantly increases after breakfast. Breathing activity diminished
during the day and reached its minimum between 20:00 and
24:00 hours. The percentage of time spent breathing rose significantly between 04:00 and 07:00 hours, when mothers were asleep.
(Adapted with permission from Patrick J, Campbell K, Carmichael L,
et al: Patterns of human fetal breathing during the last 10 weeks of
pregnancy, Obstet Gynecol. 1980 Jul;56(1):24–30.)Antepartum Fetal Assessment 387
CHAPTER 20
■ Fetal Heart Rate Acceleration
Autonomic inuences are mediated by sympathetic or parasympathetic impulses rom brainstem centers to normally raise
or slow the etal heart rate. Te NS is based on the hypothesis
that the heart rate o a etus that is not acidemic as a result o
hypoxia or neurological depression will temporarily accelerate
in response to fetal movement (American College of Obstetricians and Gynecologists, 2019; Lee, 1975). Fetal movements
during testing are identied by maternal perception and selfrecorded. As hypoxia develops, etal heart rate accelerations
diminish (Smith, 1988).
Gestational age inuences acceleration of the fetal heart rate.
Pillai and James (1990b) studied patterns o etal heart rate
acceleration during normal pregnancy. Te percentage o body
movements accompanied by accelerations and the amplitude o
these waveorms both increase with gestational age (Fig. 20-5).
Accordingly, the National Institute o Child Health and
Human Development Fetal Monitoring Workshop dened
acceleration waveorms based on gestational age (Macones,
2008). In etuses at or beyond 32 weeks’ gestation, the acceleration acme is ≥15 beats per minute (bpm) above the baseline
rate, and the acceleration lasts ≥15 seconds but <2 minutes.
Before 32 weeks, accelerations are dened as having a rise
≥10 bpm above baseline or ≥10 seconds. In one study o 188
nor mal etuses at 25 and 28 weeks’ gestation, only 70 percent
demonstrated the required ≥15 bpm during heart rate accelerations. Accelerations of 10 bpm occurred in 90 percent (Guinn,
1998). Cousins and associates (2012) compared the Workshop criteria recommended beore 32 weeks with the standard
15 bpm/15 second criteria in a randomized trial of 143 women.
Tey ound no diferences in perinatal outcomes.
■ Reactive (Normal) Nonstress Tests
A normal NS is termed reactive and requires two or more
accelerations within 20 minutes o beginning the test (Fig. 20-6)
(American College of Obstetricians and Gynecologists, 2021a).
Accelerations are accepted irrespective o etal movement. Beore
concluding that a test is nonreactive, a 40-minute or longer tracing should be perormed. Tis threshold accounts or etal sleep
cycles (Paul, 1995). Miller and coworkers (1996b) reviewed outcomes in etuses with NS results that were considered nonreactive because only one acceleration was recorded. Tey concluded
that one acceleration was as reliable as two in predicting healthy
etal status. NSs are more likely to be reactive and have a
shorter testing time in the evening compared with the morning
(Babazadeh, 2005; Petrikovsky, 1996).
Loud external sounds have been used to startle the etus
and thereby provoke heart rate acceleration. A commercially
available acoustic stimulator is positioned on the maternal
abdomen, and a stimulus o 1 to 2 seconds is applied (Eller,
1995). Tis may be repeated up to three times or up to 3
seconds (American College of Obstetricians and Gynecologists, 2021a). In a randomized trial o 113 women undergoing NS, vibroacoustic stimulation lowered the average
testing time and incidence o nonreactive test results (PerezDelboy, 2002; Turitz, 2012). One case report described a
etal tachyarrhythmia that was provoked with vibroacoustic
stimulation in a etus with known premature atrial contractions (Laventhal, 2003).
Although a normal number and amplitude o accelerations seems to reect etal well-being, their absence does not
100
90
80
70
60
50
40
30
20
10
0
16 20 24 28 32 36 40
Fetuses with accelerations (percent)
Weeks’ gestation
FIGURE 20-5 Percentage of fetuses with at least one acceleration
of 15 bpm sustained for 15 seconds concurrent with fetal movement. (Redrawn from Pillai M, James D: The development of fetal
heart rate patterns during normal pregnancy, Obstet Gynecol. 1990
Nov;76(5 Pt 1):812–816.)
FIGURE 20-6 Reactive nonstress test. Notice there are at least two fetal heart rate accelerations (arrows) of more than 15 beats/min for
longer than 15 seconds. The black line reflects fetal heart rate, whereas the purple line reflects the mother’s.388 The Fetal Patient
Section 6
invariably predict etal compromise.
Indeed, some investigators have reported
alse-positive rates ≥90 percent (Devoe,
1986). Because healthy etuses may not
move or up to 75 minutes, some have
considered that a longer NS duration might increase the positive predictive value o the NS (Brown, 1981).
In this scheme, either the test became
reactive during a period up to 80 minutes or the test remained nonreactive or
120 minutes, which indicated a very ill
etus. Tereore, prolonged etal heart
rate monitoring is undertaken i an NS
remains nonreactive after 40 minutes.
■ Nonreactive (Abnormal)
Nonstress Tests
Based on the oregoing, a nonreactive
NS is not always ominous and can
be seen with a sleeping etus. An NS
result can also revert to normal as the
etal condition changes. An example is
shown in Figure 20-7. Instead, a reactive NS result can become abnormal i
the etal condition deteriorates.
Some abnormal patterns reliably orecast severe etal jeopardy (Fig. 20-8). For
example, Devoe and colleagues (1985)
concluded that >90 percent o NS
results that were nonreactive or 90 minutes or more were associated with signi-
icant perinatal pathology. Specically,
Visser and associates (1980) described a
terminal cardiotocogram, which included:
60
90
150
120
180
210
240
30
60
90
150
120
180
210
240
30
20
0
40
60
80
100
20
0
40
60
80
100
60
90
150
120
180
210
240
30
60
90
150
120
180
210
240
30
A B
FIGURE 20-7 Two antepartum fetal heart rate (FHR) tracings in a 28-week pregnant
woman with diabetic ketoacidosis. A. FHR tracing (upper panel) and accompanying
contraction tracing (second panel). Tracing, obtained during maternal and fetal acidemia, shows absence of accelerations, diminished variability, and late decelerations with
weak spontaneous contractions. B. Fetal heart rate tracing shows return of normal
accelerations and variability of the fetal heart rate following correction of maternal
acidemia.
20
0
40
60
80
100
20
0
40
60
80
100
60
90
150
120
180
210
240
30
60
90
150
120
180
210
240
30
Nonstress Test
45 minute mark
Time: 0415 hr
119 91
Oxytocin Challenge Test
Dosage: 8 mU/min
Time: 0615 hr
Cesarean Section: 0650 hr
FHR 110 BPM
Apgar 1/0
Umbilical vein pH = 6.58
FIGURE 20-8 Nonreactive nonstress test (left side of tracing) followed by contraction stress test showing mild, late decelerations (right side
of tracing). Cesarean delivery was performed, and the severely acidemic fetus could not be resuscitated.Antepartum Fetal Assessment 389
CHAPTER 20
(1) baseline variability <5 bpm, (2) absent accelerations, and (3)
late decelerations with spontaneous uterine contractions. Tese
mirrored experiences rom Parkland Hospital in which absence o
accelerations during an 80-minute recording period in 27 etuses
was associated consistently with evidence o uteroplacental pathology (Leveno, 1983). Te latter included etal-growth restriction
in 75 percent, oligohydramnios in 80 percent, etal acidemia in
40 percent, meconium in 30 percent, and placental infarction in
93 percent.
■ Interval Between Testing
Set originally and arbitrarily at 7 days, the interval between
NSs varies based on indication (Paul, 1995). According to the
American College of Obstetricians and Gynecologists (2021a),
weekly testing is undertaken in the setting o stable maternal
medical conditions such as pregestational diabetes, chronic
hypertension, or lupus. For high-risk conditions such as preeclampsia remote rom term, some perorm NSs daily. Fetal
conditions require individualized periodic testing based on the
etal complication. Fetal-growth restriction is a common indication for which testing intervals vary (Fig. 47-6, p. 829).
■ Decelerations During Nonstress Testing
Fetal movements commonly produce heart rate decelerations.
In one study o 16 near-term etuses, one hal to two thirds
o NS tracings had decelerations, depending on the vigor o
the etal motion (imor-ritsch, 1978). Tis high incidence
o decelerations inevitably makes interpretation o their signicance problematic. Indeed, Meis and coworkers (1986)
reported that variable etal heart rate decelerations during
NSs were not a sign o etal compromise. Te American College of Obstetricians and Gynecologists (2021a) has concluded
that variable decelerations, if nonrepetitive and brief—less than
30 seconds—do not indicate fetal compromise or the need for
obstetrical intervention. Repetitive variable decelerations—at
least three in 20 minutes—have been associated with a greater
risk of cesarean delivery for fetal distress. Decelerations lasting
≥1 minute are reported to have an even worse etal prognosis
(Bourgeois, 1984; Druzin, 1981; Pazos, 1982).
Hoskins and associates (1991) attempted to rene interpretation o tests that showed variable decelerations by adding
sonographic estimation o amnionic uid volume. Te incidence
o cesarean delivery or intrapartum etal distress progressively
rose concurrently with the decline o amnionic uid volume.
Variable decelerations during an NS plus oligohydramnios
resulted in a 75-percent cesarean delivery rate. Fetal distress in
labor, however, also frequently developed in those pregnancies
with variable decelerations but with normal amounts o amnionic uid. Others report similar results (Grubb, 1992).
■ Falsereactive Nonstress Tests
In one review o etal death within 7 days o a reactive NS, the
most frequent indication for testing was postterm pregnancy
(Smith, 1987). Te mean interval between testing and death
was 4 days, with a range of 1 to 7 days. e single most common autopsy nding was meconium aspiration, often associated with some type o umbilical cord abnormality. Te authors
concluded that acute asphyxia had provoked etal gasping. Tey
considered an NST inadequate to preclude an acute asphyxial
event, but viewed amnionic uid volume assessment as valuable. Other ascribed frequent causes of fetal death despite a
alse-reactive NS included intrauterine inection, abnormal
cord position, etal malormations, and placental abruption.
BIOPHYSICAL PROFILE
Assessing ve specic fetal biophysical variables more accurately
predicts etal health (Manning, 1980). Tese include heart rate
acceleration, breathing, movement, tone, and amnionic uid
volume (Table 20-2). In the commonly used biophysical profle (BPP), each normal variable is assigned a score o 2, and
abnormal variables are given a score o 0. Tus, the highest
score possible or a normal etus is 10. Because etal breathing
and movement are episodic, 30 minutes are allotted to per-
orm a BPP beore a score o 0 is assigned to any component.
Figure 20-9 shows color Doppler evidence of amnionic uid
owing through the nares with etal breathing. In one study,
BPP scores were higher i a test was perormed in late evening
compared with the morning (Ozkaya, 2012). Narcotics and
sedatives can signicantly lower the score (Kopecky, 2000).
Using the BPP interpretation and management strategy
shown in Table 20-3, Manning and colleagues (1987) evaluated more than 19,000 pregnancies. Greater than 97 percent
o the tested pregnancies had normal results. Tey reported a
TABLE 20-2. Components and Scores for the Biophysical Profile
Component Score 2 Score 0
Nonstress testa ≥2 accelerations within 20–40 min 0 or 1 acceleration within 20–40 min
Fetal breathing ≥1 episode of rhythmic breathing lasting ≥30 sec <30 sec of breathing
Fetal movement ≥3 discrete body or limb movements <3 discrete movements
Fetal tone ≥1 episode of extremity extension and subsequent return
to flexion
0 extension/flexion events
Amnionic fluid
volumeb
A pocket of amnionic fluid that measures at least 2 cm in
two planes perpendicular to each other (2 × 2 cm pocket)
Deepest single vertical pocket ≤2 cm
aMay be omitted if all four sonographic components are normal.
bFurther evaluation warranted, regardless of biophysical composite score, if deepest vertical amnionic fluid pocket ≤2 cm.390 The Fetal Patient
Section 6
false-normal test rate—dened by an antepartum death of a
structurally normal fetus—that approximated 1 per 1000. e
most common identiable causes of fetal death after a normal
BPP score include etomaternal hemorrhage, umbilical cord
accident, and placental abruption (Dayal, 1999).
Subsequently, Manning and associates (1993) published a
remarkable description of 493 fetuses in which BPP scores were
correlated with umbilical venous blood pH values. Tis blood was
being obtained via antepartum cordocentesis for other specic
etal indications. Namely, karyotyping o etal-growth restricted
etuses constituted 20 percent, and the remainder had alloimmune hemolytic anemia requiring hemoglobin measurement.
As shown in Figure 20-10, a BPP score o 0 was almost invariably associated with signicant fetal acidemia, whereas a normal
score of 8 or 10 was associated with normal pH. An equivocal
test result—a score of 6—was a poor predictor of an abnormal
outcome. A drop in the BPP score from 2 or 4 down to 0 more
accurately predicted an abnormal fetal outcome. Overall, BPP
scores provided poor sensitivity to predict cord blood pH. Similar studies have concluded the same (Salvesan, 1993; Weiner,
1996). Kaur and colleagues (2008) perormed daily BPPs to
ascertain the optimal delivery time in 48 growth-restricted
preterm etuses that weighed <1000 g. Despite scores of 8 in
27 etuses and 6 in 13 others, 6 died and 21 were acidemic.
■ Modified Biophysical Profile
BPP performance is labor intensive and requires a trained
sonographer. In response, Clark and coworkers (1989) created
FIGURE 20-9 A sagittal color Doppler image displays the movement of amnionic fluid through the nares during fetal breathing.
TABLE 20-3. Interpretation of Biophysical Profile Score
Biophysical Profile Score Interpretation Recommended Management
10 Normal, nonasphyxiated fetus No fetal indication for intervention; repeat test weekly
8/10 (Normal AFV)
8/8 (NST not done)
Normal, nonasphyxiated fetus No fetal indication for intervention; repeat test weekly
8/10 (Decreased AFV) Chronic fetal asphyxia suspected If ≥36 weeks, deliver
If <36 weeks, monitor per institution's protocol
6 (Normal AFV) Equivocal If ≥37 weeks, deliver
If <37 weeks and normal fluid, repeat test in 24 hours
If repeat test >6, monitor per institution's protocol
6 (Decreased AFV) Possible fetal asphyxia If 36–37 weeks, deliver
If <36 weeks, monitor per institution's protocol
4 Probable fetal asphyxia If ≥32 weeks, deliver
If <32 weeks, individualize management based on maternal
and fetal conditions
0 or 2 Almost certain fetal asphyxia Deliver
AFV = amnionic fluid volume; NST = nonstress test.
Adapted from American College of Obstetricians and Gynecologists, 2021a; Liston, 2018; Manning, 2018.
7.40
7.35
7.30
7.25
7.20
7.10
7.05
10 8 6 4 2 0
*
*
*
*
Fetal biophysical profile score
Antepartum umbilical venous pH
FIGURE 20-10 Mean umbilical vein pH (±2 SD) obtained by
cordocentesis in relation to fetal biophysical profile score category.
(Data from Manning, 1993.)Antepartum Fetal Assessment 391
CHAPTER 20
an abbreviated BPP, in which an NS was coupled with amnionic uid volume assessment. In 2628 singleton pregnancies,
the NST was performed twice weekly. Described in the next
section, amnionic uid volume was measured by the amnionic
uid index (AFI), and values ≤5 cm were considered abnormal. is abbreviated BPP required approximately 10 minutes
to perorm. Te authors considered it a superb antepartum surveillance method because no etuses died unexpectedly.
From another study of 17,429 modied BPPs in 2774
women, investigators concluded that such testing was an
excellent fetal surveillance tool (Nageotte, 1994). Miller and
associates (1996a) reported results of more than 54,000 modi-
ed BPPs performed in 15,400 high-risk pregnancies. ey
described a alse-negative rate o 0.8 per 1000 and a alsepositive rate of 1.5 percent. e American College of Obstetricians and Gynecologists (2021a) has concluded that the BPP
and modied BPP are comparable to other biophysical fetal
surveillance approaches in predicting etal well-being.
AMNIONIC FLUID VOLUME
Te importance o amnionic uid volume estimation is indicated by its inclusion into virtually all schemes o etal health
assessment (Frøen, 2008). Physiologically, diminished uteroplacental perusion may lead to lower etal renal blood ow,
decreased urine production, and ultimately, oligohydramnios
(Chap. 14, p. 260). Amnionic uid volume is measured either
by the AFI or by the single deepest vertical pocket (DVP). In
one study o more than 1000 women in which both methods
were compared, AFI led to a higher rate o oligohydramnios
diagnoses and induction of labor. Despite this, perinatal outcomes were not improved (Kehl, 2016). Te American College of Obstetricians and Gynecologists (2021a) concludes that
DVP measurement, as opposed to AFI, is associated with fewer
unnecessary interventions but comparable perinatal outcomes
(Nabhan, 2008; Reddy, 2014). An AFI ≤5 cm and a DVP
≤2 cm is considered abnormal.
DOPPLER VELOCIMETRY
Blood ow velocity measured by Doppler ultrasound reects
downstream impedance (Chap. 14, p. 261). is Doppler
velocimetry has been used to interrogate the umbilical artery,
middle cerebral artery (MCA), and ductus venosus. With
umbilical artery studies, abnormal waveorms correlated with
placental villous hypovascularity. Specically, of the small placental arterial channels, 60 to 70 percent must be obliterated
before the umbilical artery Doppler waveform becomes abnormal. Such extensive placental vascular pathology has a major
efect on etal circulation. According to rudinger (2007),
because more than 40 percent of the combined fetal ventricular
output is directed to the placenta, obliteration o placental vascular channel increases aterload and leads to etal hypoxemia.
Tis in turn leads to ventricular dilation and redistribution o
MCA blood ow. Ultimately, pressure rises in the ductus venosus due to aterload in the right side o the etal heart (Baschat,
2004). Clinically, abnormal Doppler waveforms in the ductus
venosus are a late nding in the progression of fetal deterioration due to chronic hypoxemia. o predict placental dysunction, maternal uterine artery Doppler velocimetry also has been
assessed, with the goal to balance stillbirth against the risks o
preterm delivery (Ghidini, 2007).
■ Umbilical Artery
e umbilical artery systolic-diastolic (S/D) ratio is considered abnormal i it is above the 95th percentile or gestational
age or if diastolic ow is either absent or reversed (Chap. 14,
p. 262). Absent or reversed end-diastolic ow signies greater
impedance to umbilical artery blood ow (Fig. 47-7, p. 830).
It is reported to result rom poorly vascularized placental villi
and is seen in extreme cases o etal-growth restriction (odros,
1999). Te perinatal mortality rate is increased when absent or
reversed end-diastolic ow is present (Viero, 2004).
Umbilical artery Doppler velocimetry to evaluate fetal health
has been extensively assessed in randomized trials. In one, 1360
women with a high risk or stillbirth underwent either an NS
or Doppler velocimetry, and abnormal results prompted labor
induction. More patients in the Doppler group required induction, yet the cesarean delivery rate or intrapartum etal distress was 4.6 percent. is rate was signicantly lower than the
8.7-percent cesarean rate or those receiving an NS (Williams,
2003). e authors believed that Doppler assessment, compared with an NST, identied a higher proportion of patients
with early placental compromise. Identied early, these fetuses
experienced less distress, which yielded a lower cesarean delivery rate. Similarly, Yoon and coworkers (1992) ound that the
BPP and umbilical artery Doppler measurements are comparable indicators of fetal acidosis. Introduction of Doppler velocimetry as a primary screening test must balance any advantages
against its necessary training and associated costs.
In addition, umbilical artery Doppler velocimetry does
not efectively predict etal health in normal pregnancies
(Alrevic, 2015; Page, 2017). Gonzalez and associates (2007)
found that abnormal umbilical artery Doppler ndings in a
cohort o growth-restricted etuses were the best predictors
of perinatal outcomes. e American College of Obstetricians and Gynecologists (2021a) has concluded that umbilical artery Doppler velocimetry has not proved valuable as
a screening test, except in cases o etal-growth restriction
(Chap. 47, p. 830).
■ Ductus Venosus
Doppler ultrasound can also assess the fetal venous circulation,
and as discussed earlier, an abnormal ductus venosus Doppler
waveorm indicates cardiac dysunction. However, its routine
use in surveillance o etal-growth restriction is not recommended (Society or Maternal-Fetal Medicine, 2020).
Ductus venosus Doppler is also used in the staging of twintwin transfusion syndrome (Quintero, 1999). Abnormal Doppler indices reect myocardial dysunction and predict a poorer
outcome (Banek, 2003). Additionally, this Doppler method can
help monitor etuses with congenital heart deects and supraventricular tachycardia (SV) (Seravalli, 2016). Namely, SV can
induce a reversible cardiomyopathy that may lead to hydrops.392 The Fetal Patient
Section 6
Ductus venosus Doppler patterns may aid prediction and monitor improvement ollowing treatment. Tus, ductus venosus
Doppler may have a role in monitoring pregnancies at increased
risk or etal cardiovascular decline (Baschat, 2010).
■ Middle Cerebral Artery
Doppler velocimetry of the MCA is the primary method of
detecting fetal anemia (Chap. 14, p. 263). With fetal anemia,
the peak systolic velocity is enhanced due to greater cardiac output and decreased blood viscosity. However, to detect etal
compromise, Doppler velocimetry of the MCA is not recommended (Morris, 2012). In one randomized study o 665
women assigned to modied BPP alone or to modied BPP
plus MCA and umbilical artery Doppler velocimetry, pregnancy outcomes did not dier (Ott, 1998).
■ Uterine Artery
Vascular resistance in the uterine circulation normally declines
in the rst half of pregnancy. is stems from trophoblast
invasion and remodeling o maternal uterine vessels (Chap. 5,
p. 90). Uterine artery Doppler velocimetry may be most help-
ul in assessing pregnancies at high risk o uteroplacental insu-
ciency (Abramowicz, 2008). Persistence or development of
high-resistance patterns has been linked to various pregnancy
complications (Sciscione, 2009; Velathur, 2014). In a study of
30,519 unselected British women, uterine artery velocimetry
was assessed at 22 to 24 weeks’ gestation (Smith, 2007). e
risk o etal death beore 32 weeks, when associated with abruption, preeclampsia, or fetal-growth restriction, was signicantly
linked to high-resistance ow. However, technique standards
and criteria to dene an abnormal test are lacking. us, uterine artery Doppler studies are not considered standard practice
in either low- or high-risk populations (Society or MaternalFetal Medicine, 2020).
ANTENATAL TESTING SUMMARY
Despite a continuous evolution of options, the precision of any
given method is limited. Moreover, the wide range o normal
biological etal variation makes interpretation o test results
challenging. Tis prompts many clinicians to use antenatal testing to orecast etal wellness rather than illness.
Antenatal testing ecacy was reviewed between 1971 and
1985 at Los Angeles County Hospital (Platt, 1987). Nearly
17,000 women underwent antepartum testing o various types.
Fetal surveillance rose rom <1 percent o pregnancies in the
early 1970s to 15 percent in the mid-1980s. Tese authors
concluded that such testing was clearly benecial because the
fetal death rate was signicantly less in the tested high-risk
pregnancies compared with the rate in those not tested. Te
study, however, did not consider other innovations incorporated into practice during those years. Results from Ghana
suggest that NSTs may be benecial in low-resource countries (Lawrence, 2016). Namely, in an observational study o
316 pregnancies complicated by gestational hypertension,
women undergoing an NST had a nonsignicant decreased
risk for stillbirth compared with those not tested—3.6 versus
9.2 percent, respectively. However, the benets of antenatal fetal
testing have not been suciently evaluated in randomized trials.
Another important and unanswered question is whether antepartum fetal surveillance identies fetal asphyxia early enough to
prevent brain damage. Manning and associates (1998) studied
the incidence o cerebral palsy in 26,290 high-risk pregnancies
managed with serial BPP testing. Tese outcomes were compared with those o 58,657 low-risk pregnancies in which antepartum testing was not perormed. Te rate o cerebral palsy was
1.3 per 1000 in tested pregnancies compared with 4.7 per 1000
in untested women. odd and colleagues (1992) attempted to
correlate cognitive development in inants up to age 2 years
following abnormal umbilical artery Doppler velocimetry or
NST results. Only abnormal NST results were associated with
marginally poorer cognitive outcomes. Tese investigators concluded that by the time etal compromise is diagnosed with
antenatal testing, etal damage has already been sustained. Low
and coworkers (2003) reached a similar conclusion.
Indications or antepartum testing include etal and maternal conditions that increase the risk or stillbirth (Table 20-4)
(American College of Obstetricians and Gynecologists, 2021b).
According to the American College of Obstetricians and Gynecologists (2021a), a normal antepartum etal test result is highly
reassuring that a stillbirth will not occur within 1 week. Tis
conclusion was reached ater an analysis o reports o stillbirth
rates associated with the various antepartum etal heart rate
tests (Table 20-5).
Te most important consideration in deciding when to
begin antepartum testing is the prognosis or neonatal survival.
Te severity o maternal disease is another. In general, with
most high-risk pregnancies, testing begins by 32 to 34 weeks’
gestation. Pregnancies with severe complications, such as fetal-growth restriction, might require testing as early as 26 to
28 weeks. e frequency for repeating tests is arbitrarily set at
7 days, but more frequent testing is often done.
TABLE 20-4. Indications for Antepartum Testing
Maternal
Chronic hypertension
Pregestational DM
SLE
Antiphospholipid
syndrome
Hemoglobinopathies
Cyanotic heart disease
Cardiomyopathy
Cystic fibrosis
Restrictive lung disease
Chronic renal disease
Hyperthyroidism
In vitro fertilization
Substance abuse
Chemotherapy (current)
Prepregnancy BMI ≥35
Maternal age >35
Pregnancy-related
Gestational hypertension
Preeclampsia
Insulin-requiring gestational DM
Oligohydramnios
Polyhydramnios
Postterm pregnancy
Prior stillbirth
Isoimmunization
Cholestasis
Velamentous cord insertion
Single umbilical artery
Fetal
Fetal-growth restriction
Decreased fetal movement
Multifetal gestation
BMI = body mass index; DM = diabetes mellitus;
SLE = systemic lupus erythematosus.
TABLE 20-5. Stillbirth Rates within 1 Week of a Normal
Antepartum Fetal Surveillance Test
Antepartum Fetal Test
Stillbirtha
Rate/1000 Number
Nonstress test 1.9 5861
Contraction stress test 0.3 12,656
Biophysical profile 0.8 44,828
Modified biophysical profile 0.8 54,617
aCorrected for lethal anomalies and unpredictable causes
of fetal death such as abruption or cord accident.
Nhận xét
Đăng nhận xét