Case 25 A 38-year-old woman with a twin pregnancy

 Case 25 A 38-year-old woman with a twin

pregnancy

Mrs Akinte is 38-year-old primigravida admitted with severe

hyperemesis which has improved with hydration and

antiemetics. She has a pelvic ultrasound which confirms a

twin pregnancy about which she is delighted as it is a

pregnancy following treatment with clomifene citrate for

anovulatory primary subfertility.

What are the predisposing factors for

twin pregnancy?

These include a family history or previous history of

multiple births, increased maternal age, ovulation induction (with clomifene 10%, with gonadotrophins 30% and

in vitro fertilization [IVF] 25 – 30%) and race (Japanese

7/1000 pregnancies, Nigerian 40/1000)

more complex depending on the timing of the division

of the embryo:

• Embryo splits at 3 days: two chorions, two amnions

(dichorionic, diamniotic)

• Embryo splits at 4 – 7 days: single placenta, one chorion,

two amnions (monochorionic, diamniotic)

• Embryo splits at 8 – 12 days (rare): single placenta,

one chorion and one amnion (monochorionic,

monoamniotic)

• Embryo splits at 13 days (very rare): conjoined or

Siamese twins

The scan shows the twins to be dichorionic and diamniotic

at 10 + 3 weeks’ gestation and the heart beat of both the

fetuses are seen. Mrs Akinte wishes to know if the twins are

identical.

How can you tell if the twins are

monozygotic or dizygotic?

While a monochorionic placentation on scan suggests

identical (monozygotic twins), with a dichorionic placenta it is not possible to determine zygosity unless the

twins are of discordant gender.

Determination of zygosity may be useful for:

• Assisting with medical decisions for the twins in later

life (e.g. to establish any genetic risk of illness)

• Participation in twin research studies

• Simply answering the inevitable questions from

friends, relatives or strangers

Zygosity can only be conclusively determined by DNA

fingerprinting, which requires amniocentesis, chorionic

villus sampling (CVS), cordocentesis and after delivery

by DNA fingerprinting of cord blood or sending a small

swab of cheek cells or a blood sample to the laboratory.

Determination of chorionicity can be performed by

ultrasonography and relies on the assessment of fetal

gender, number of placentas and characteristics of the

membrane between the two amniotic sacs. Different - sex

Obstetrics and Gynaecology: Clinical Cases Uncovered.

By M. Cruickshank and A. Shetty. Published 2009 by Blackwell

Publishing. ISBN 978-1-4051-8671-1.

KEY POINT

Twins account for about 1% of all pregnancies with

two-thirds being dizygotic and one-third monozygotic. The

incidence of triplets is 1/4000. There is increased incidence

as a consequence of assisted reproductive techniques.

Mrs Akinte wants to know the causes

for twin pregnancy and also the

different types of twins. What do you

tell her?

Twin pregnancy occurs when two or more ova are fertilized to form dizygotic (non - identical) twins, or a single

fertilized egg divides to form monozygotic (identical)

twins.

In a dizygotic twin pregnancy, each fetus has its own

placenta (either separate or fused), amnion and chorion,

whereas in a monozygotic pregnancy, the situation is160 Part 2: Cases

PART 2: CASES

twins are dizygotic and therefore dichorionic, but in

about two - thirds of twin pregnancies the fetuses are of

the same sex and these may be either monozygotic or

dizygotic (Fig. 25.1 ). Similarly, if there are two separate

placentas the pregnancy is dichorionic.

In dichorionic twins the inter - twin membrane is composed of a central layer of chorionic tissue sandwiched

between two layers of amnion, whereas in monochorionic twins there is no chorionic layer present. Dichorionic twins can be easily distinguished by the presence of

a thick septum between the chorionic sacs. This septum

becomes progressively thinner to form the chorionic

component of the inter - twin membrane, but remains

thicker and easier to identify at the base of the membrane

as a triangular tissue projection, or ‘ lambda ’ sign.

Sonographic examination of the base of the inter - twin

membrane at 10 – 14 weeks ’ gestation for the presence or

absence of the lambda sign (Fig. 25.2 ) provides reliable

distinction between dichorionic and monochorionic

pregnancies. With advancing gestation there is regression

of the chorion laeve and the ‘ lambda ’ sign becomes progressively more difficult to identify.

Mrs Akinte wishes to know the

importance of prenatal determination

of chorionicity. What information would

you give her?

Chorionicity, rather than zygosity, is the main factor

determining pregnancy outcome. In monochorionic

Figure 25.1 Dizygotic and monozygotic twins. In dichorionic twins

the inter-twin membrane is composed of a central layer of

chorionic tissue sandwiched between two layers of amnion,

whereas in monochorionic twins there is no chorionic layer

present.

Dizygotic

(non-identical)

Monozygotic

(identical)

Dichorionic

Monochorionic

Figure 25.2 Ultrasound appearance of monochorionic (left) and

dichorionic (right) twin pregnancies at around12 weeks’ gestation.

The ‘lamda’ sign is seen in the dichorionic set of twins and the ‘T’

sign (with the very thin inter-twin membrane) in the

monochorionic set of twins.

(a)

(b)Case 25 161

PART 2: CASES

twins the rates of miscarriage, perinatal death, preterm

delivery, fetal growth restriction and fetal abnormalities

are much higher than in dichorionic twins. Death of a

monochorionic fetus is associated with a high chance of

sudden death or severe neurological impairment in the

co - twin.

Twin – twin transfusion syndrome (TTTS), an imbalanced flow of blood from one twin to another, occurs in

10 – 15% of monozygotic twins who share a placenta (Fig.

25.3 ). The implications of this are very serious for the

survival (perinatal mortality of >80%) and health of both

twins and they would require close monitoring during

the pregnancy.

In view of her age, Mrs Akinte is

concerned about the risk of Down’s

syndrome. What screening

investigations would you offer her?

Fetal abnormality is more common in multiple pregnancies – both the maternal age - specific chromosomal disorders (as increasing maternal age is a risk factor for

multiple birth) and fetal anatomical disorders (seen more

with monochorionic than dichorionic twins).

Serum screening in multiple pregnancy is not reliable,

as it may identify only about 45% of affected fetuses for

a 5% false positive rate. Nuchal translucency (NT) assessment (ultrasound measurement of the translucency of

the nuchal fold in the fetal neck between 10 and 14

weeks) identifies about 70% of individual fetuses at high

risk of trisomy and is an option for screening with multiple pregnancies.

Invasive prenatal diagnosis is challenging as there are

at least two fetuses to sample correctly and should be

undertaken in a tertiary referral centre. The procedure

chosen will depend on chorionicity. Both amniocentesis

and CVS risk contamination – amniocentesis where

double sac sampling occurs and CVS where chorions are

not separately sampled. Procedure - related miscarriage

rates appear to be similar to those for singleton

pregnancies.

Figure 25.3 Twin–twin transfusion syndrome (TTTS). In the larger

recipient there is usually a large bladder and polyhydramnios and

the smaller anuric donor is held fixed to the placenta by the

collapsed membranes of the anhydramniotic sac.

KEY POINT

If one fetus is detected as abnormal, selective termination

(if desired) with intracardiac potassium chloride in

dichorionic twins must be accurately targeted. Selective

termination in monochorionic pregnancies risks co-twin

sequelae, but cord occlusion can be considered.

Mrs Akinte opts to have the NT scan at 12 weeks which

shows the fetuses to be at low risk for Down’s syndrome.

She asks about the risks associated with multiple pregnancy.

What do you tell her?

Multiple pregnancies are considered high - risk because:

• Increased risk of prematurity – the mean gestation for

twins is 37 weeks and for triplets 31 weeks

• Higher risk of congenital abnormality associated with

multiple pregnancies (×2 – 4 the rate in singleton

pregnancies)

• Higher rates of cerebral palsy found in twins (1 – 1.5%)

and triplets (7 – 8%)

• Perinatal mortality rate for twins is significantly higher

than singletons (×5) and even higher for triplets (×6).

• Smaller babies – fetuses tend to be individually smaller

than those in a singleton pregnancy because of greater

demand for nutrients and slower in utero growth, i.e.

light - for - dates. Monozygotic twins tend to be smaller

than dizygotic twins.

• Death of one fetus. Death of one fetus in dichorionic

pregnancies carries a risk of death or handicap of 5 – 10%

to the remaining fetus. This is mainly because of preterm

delivery, which may be the consequence of release of

cytokines and prostaglandins by the resorbing dead

placenta. In monochorionic twins, there is at least a 30%

risk of death or neurological handicap to the co - twin

because, in addition to preterm delivery, there is a risk of162 Part 2: Cases

PART 2: CASES

acute hypotensive episodes as a result of haemorrhage

from the live fetus into the dead fetoplacental unit

(Box 25.1 ).

• Higher rate of maternal pregnancy - related complications such as hyperemesis gravidarum, miscarriage, polyhydramnios, pre - eclampsia, anaemia and antepartum

haemorrhage.

• Higher rate of complications in labour – malpresentation, vasa praevia, cord prolapse, premature separation of

placenta, cord entanglement and postpartum haemorrhage (PPH).

Mrs Akinte wants some information on

support groups. What support groups

do you know of?

• TAMBA: Twin and multiple birth association

• The Multiple Birth Foundation

• The UK Twin to Twin Transfusion Syndrome

Association

What kind of antenatal care can she

expect during this twin pregnancy?

• Detailed anomaly scan at 18 – 20 weeks.

• Cervical length scan at 20 – 24 weeks to determine the

risk of preterm labour. Cervical length <2.5 mm is associated with increased risk of preterm labour, hence prophylactic steroids could be offered. There is not enough

evidence about the role of cervical cerclage, but this too

could be offered.

• Regular scans every 4 weeks after about 24 weeks until

32 weeks, to monitor growth and fetal well - being, thereafter 2 - weekly until 36 weeks. From 36 week onwards

umbilical artery Doppler scan and amniotic fluid volume

should be performed weekly (Box 25.2 ).

• Anaemia should be looked for and treated vigorously.

• Monitor for early signs of pre - eclampsia.

Her 20-week detailed anomaly scan was normal. The

24-week scan showed normal growth of both the twins

with normal liquor volume. The cervical length was found to

be 41mm which is within normal limits. Her husband works

offshore.

She is keen to know her likelihood

of having a full-term pregnancy and

how big the babies are likely to be

when born?

See Table 25.1 .

Box 25.1 Complications specific to

monochorionic twin pregnancy

Twin–twin transfusion syndrome (TTTS) with placental

vascular anastomosis with unequal distribution of blood

between the twins. Approximately 10–15% of

monochorionic twin pregnancies may be affected with

TTTS. The donor twin becomes anaemic, hypovolaemic,

oligohydramniotic and growth restricted. The recipient

becomes polycythaemic, hypovolaemic and polyuric with

polyhydramniosis and hydrops.

Twin reversed arterial perfusion sequence (TRAP) is

found in approximately 1% of monozygotic twin

pregnancies (acardiac twinning). The underlying

mechanism is thought to be disruption of normal vascular

perfusion and development of the recipient twin because

of an umbilical arterial–arterial anastomosis with the donor

or pump-twin.

Box 25.2 Management of twin pregnancies

Monochorionic twins should be scanned fortnightly from

16 weeks to detect twin–twin transfusion syndrome

(TTTS). The pathognomonic features of severe TTTS by

ultrasonographic examination are the presence of a large

bladder in the polyuric recipient fetus in the

polyhydramniotic sac and ‘absent’ bladder in the anuric

donor which is much smaller than the recipient (Fig. 25.2).

If suspected, these pregnancies should be referred to

tertiary fetal medicine centres for further management –

first line management is usually laser surgery of inter-twin

vascular placental anastomoses where the syndrome

develops before 26 weeks’ gestation, other options include

serial amnioreduction or elective delivery.

Table 25.1 Gestation periods for multiple births.

Average length of

pregnancy (weeks)

Average birth

weight (kg)

Singletons 40 3.5

Twins 37 2.5

Triplets 34 1.8

Quads 32 1.4Case 25 163

PART 2: CASES

Mrs Akinte is seen at the clinic at 28 weeks, and the growth

scan shows the abdominal circumference of both the fetuses

to be on the 50th centile with normal liquor volumes. Twin

1, which is the leading twin, was transverse and twin 2 was

breech. Mrs Akinte is anxious about the presentation of the

fetus and having a caesarean section.

How would you counsel her?

As Mrs Akinte is only 28 weeks at present, it is highly

likely that the lie and presentation might change as the

pregnancy advances. She could attempt a trial of vaginal

delivery provided the first twin is a cephalic presentation

and there are no other complicating factors. Where the

first twin is presenting as breech or as a transverse lie,

caesarean section is the preferred mode of delivery.

Her 32- and 34-week scans show normal growth and

normal liquor of both the twins. At 36 weeks abdominal

circumference of twin 1 is on 50th centile but twin 2’s

abdominal circumference is just above 10th centile. The

liquor volume of both the twins is normal and there is good

end diastolic flow on the umbilical artery Doppler scan. The

presentation of twin 1 is cephalic and that of twin 2 breech.

How would you manage her?

Repeat umbilical artery Doppler scan in a week ’ s time at

37 weeks.

Mrs Akinte feels good fetal movements for both twins. On

scan twin 1’s abdominal circumference is still on 50th centile

but twin 2’s abdominal circumference is now on the 5th

centile with static growth. Twin 1 is still cephalic and twin 2

is breech.

What would you advise her?

Admission to the ward for induction of labour because

of static growth of twin 2. If the cervix is unfavourable,

prostaglandins would be indicated for induction of

labour, if favourable, artificial rupture of membranes

(ARM) with oxytocin augmentation could be

performed.

Consider induction of labour for pregnancy complications. It is uncommon for twin pregnancies to be allowed

to progress beyond 40 completed weeks. There are insufficient data available to support a practice of elective

delivery from 37 weeks ’ gestation for women with an

otherwise uncomplicated twin pregnancy at term

although the general practice is to deliver by 37 – 39

weeks.

Mrs Akinte’s cervix is 3cm dilated and favorable. She has an

ARM and oxytocin is commenced. Both the fetuses are

monitored continuously by cardiotocography (CTG). She

wishes to have an early epidural for pain relief which is

organized.

What would be your intrapartum

management?

Obtain IV access, FBC, group and save, monitor fetal

heart rates separately and check position of lead fetus.

In most cases, vaginal birth proceeds as normal.

Immediately after first baby is born determine the position of the second fetus by abdominal and vaginal examination with or without ultrasound. Rupture the second

amniotic sac (once the presenting part is fixed in the

pelvis) and proceed to delivery (as either breech or

cephalic).

If transverse, external cephalic or internal podalic

version can be attempted to bring the baby into a longitudinal lie. A caesarean section for the second twin may

be indicated if version is unsuccessful or if there is fetal

distress.

Oxytocin augmentation of uterine contractions may

be required after delivery of twin 1. The second twin

usually delivers within 20 – 45 minutes of the first twin,

although this can vary.

The question of whether all women with twin pregnancies should have a caesarean section is contentious.

Current NICE guidance recognizes that in uncomplicated twin pregnancies at term with a cephalic first twin,

the second twin nonetheless has a higher risk of perinatal

morbidity and mortality – whether section for the second

twin improves outcome is uncertain and therefore

should not be routinely offered, except as part of

research.

Third stage should be actively managed by IM injection of syntometrine or syntocinon to avoid PPH.

KEY POINT

Monochorionic, monoamniotic placentation is found in

approximately 1% of all twin gestations. High mortality

rates (up to 50%) have been attributed to cord

entanglement, knots and twists, congenital anomalies and

prematurity.164 Part 2: Cases

PART 2: CASES

CASE REVIEW

Mrs Akinte had an early diagnosis of a dichorionic twin

pregnancy at 10 weeks ’ gestation. She opted to have nuchal

scans on the twins which gave both the twins a low risk for

Down ’ s syndrome. She was given information about the

support groups, risks of twin pregnancy, antenatal management and intrapartum care plans. The detailed scan,

booking bloods and all the growth scans up until 34 weeks

were normal. Twin 2 ’ s growth began to tail off towards 36

weeks and was static by 37 weeks, and delivery was planned.

As twin 1 was in a cephalic presentation, Mrs Akinte opted

for a vaginal delivery. Labour was induced with an ARM

and oxytocin and progressed normally and she delivered

both babies vaginally. The third stage was managed actively

with acceptable blood loss of 700 mL.

KEY POINTS

• When a multiple gestation has been diagnosed every

effort should be made to determine chorionicity at the

time of diagnosis. The optimal time to determine

chorionicity is 10–14 weeks

• Biochemical screening for aneuploidy is not

recommended in twins. NT screening is useful for

identifying twin pregnancies at high risk of aneuploidy

• Invasive prenatal diagnosis is technically more demanding

in multiple pregnancies than singleton pregnancies

• Routine hospitalization for bed rest in multiple gestation

is not recommended. There is insufficient evidence to

support prophylactic activity restriction or work leave in

multiple gestation

• An 18–22 week detailed anomaly scan is advised

• Serial ultrasonographic evaluation every 4 weeks is

indicated in dichorionic twin gestations to confirm

normal growth and fornightly in uncomplicated

monochorionic twin pregnancy to look for features

suggestive of TTTS and to monitor growth

• Multiple pregnancies are associated with increased risks

of antenatal complications such as miscarriage, preterm

birth, intrauterine growth restriction, anaemia,

pre-eclampsia, antepartum haemorrhage and gestational

diabetes

• For otherwise uncomplicated twin pregnancies, delivery

should be considered at 38–39 weeks

• Vaginal delivery is an appropriate mode of delivery for

uncomplicated twin pregnancies with the first twin in

vertex presentation. The clinical indications for elective

caesarean section in twin gestations include a non-vertex

first twin and monoamniotic twins