Case 62: Twin pregnancy

 

Case 62: Twin pregnancy

CASE 62: TWIN PREGNANCY

History

A 37-year-old woman attends the antenatal clinic at 18 weeks’ gestation. She is gravida 2

para 1, having had a spontaneous vaginal delivery at term 8 years ago. This current pregnancy was achieved through in vitro fertilization after four attempts (cycles). Two embryos

were implanted. The first-trimester scan confirmed a twin gestation and noted a lambda sign

between the gestations sacs. The anomaly scan is due in 2 weeks.

So far the woman has been feeling nauseated and tired but well.

Examination

The blood pressure is 120/78 mmHg. The fundus is palpable 2 cm above the umbilicus. Two

separate fetal hearts are heard on hand-held fetal Doppler, one 143/min, the other 130/min.

INVESTIGATIONS

Normal range for

pregnancy

Haemoglobin 9.8 g/dL 11–14 g/dL

Mean cell volume 71 fL 74.4–95.6 fL

White cell count 5.3×109/L 6–16×109/L

Platelets 204×109/L 100–400×109/L

Urinalysis: negative

Haemoglobin electrophoresis: sickle trait (AS)

Blood group: A positive

Rubella antibody: immune

HIV1/2: negative

Hepatitis B: negative

Syphilis: negative

Twelve-week transabdominal ultrasound scan report: two viable fetuses present,

measuring 82 and 80 mm.

Questions

• How would you interpret the results?

• What can the parents be told about the zygosity of the pregnancy?

• How would you monitor and manage this pregnancy?100 Cases in Obstetrics and Gynaecology

168

ANSWER 62

The ultrasound confirms a twin pregnancy with a lambda sign (projection of placental tissue

between the dividing membranes). This is suggestive of a dichorionic pregnancy. The woman

is anaemic with a low mean cell volume suggestive of iron-deficiency anaemia. The only other

investigation of note is that the woman has sickle trait.

Zygosity

Although the pregnancy appears dichorionic diamniotic (DCDA), this does not inform us

about zygosity. A monozygotic pregnancy may be DCDA if the embryo has split at an early

stage. One third of monozygotic pregnancies are DCDA, two-thirds monochorionic diamniotic and around 1 per cent are monochorionic monoamniotic. A single implanted embryo

may even split in an IVF pregnancy. Confirmation of zygosity is by genetic analysis, or by

observing that the fetuses are of different genders.

Monitoring

Twin pregnancies are associated with increased maternal risks of hyperemesis, anaemia, preterm labour, antepartum haemorrhage, pre-eclampsia, gestational diabetes, thrombosis and

caesarean delivery. The fetuses are at risk of intrauterine growth restriction, prematurity,

stillbirth or neonatal death, congenital anomalies and operative delivery.

! Monitoring in Twin Pregnancies

• Regular full blood count

• Close blood pressure and urinalysis monitoring

• Fetal growth surveillance from 28 weeks

• Screening for gestational diabetes

Management

In addition to routine antenatal care this woman needs:

• information regarding the increased maternal and fetal risks with twin pregnancy

• regular hospital antenatal assessment from the late second trimester

• ferrous sulphate and folic acid supplementation

• discussion of mode of delivery (depending on growth and presentation of twins at

around 36 weeks)

• hospital delivery by 40 weeks

• introduction to multiple pregnancy support groups.

The woman has sickle trait and her partner should also be tested. If he is also sickle trait

positive then prenatal testing of the babies should be offered to determine whether they are

homozygous and therefore going to be affected by sickle cell disease.

KEY POINTS

• Chorionicity and amnionicity can be determined with high accuracy by ultrasound

in the first trimester but unless the fetuses are seen to be of different sexes, the

zygosity of dichorionic diamniotic twins can only be confirmed with genetic testing.

• Multiple pregnancies are high risk for both mother and babies, and close monitoring is essential for the early detection of problems.

• A woman with sickle cell trait whose partner is also sickle cell trait positive should

be offered prenatal diagnosis by chorionic villus sampling, amniocentesis or

cordocentesis.