Multiple pregnancy

Published on 09/03/2015 by admin

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Chapter 35 Multiple pregnancy

Jackie Chua, Michael Flynn

This is considered a high-risk pregnancy because of the increased maternal and perinatal risks.

Incidence. Incidence varies with geographical location. The incidence from spontaneous conception is about 1.25% of births, from clomiphene-induced ovulation 7%, and from assisted reproductive techniques up to 10%–20%. Monozygotic twinning has an incidence of 3.5 in 1000 deliveries.

Mechanism of twinning

Dizygotic twins

• Dizygotic twins are always DCDA (dichorionic diamniotic) and account for 70% of twin pregnancies. This occurs as a result of duplication of the normal process of conception, with separate chorions, amnions and placental circulations.
• The geographic variation in the incidence of twin pregnancies is due to differences in dizygotic twinning.
• The risks for dizygotic twinning include older maternal age (>35 years), past history and family history of twinning.

Monozygotic twins

• Monozygotic twins account for 30% of twin pregnancies.
• Monozygotic twinning is determined by the timing at which splitting of the blastocyst occurs:

• before 3 days after fertilisation (about 30%): DCDA

— results in separate chorion, amnion and placental circulation

• between 4 and 8 days after fertilisation (about 70%): MCDA (monochorionic diamniotic)

— results in a single common placenta but two amnions and one chorionic membrane

• after 8 days (about 1%): MCMA (monochorionic monoamniotic)

— common amnion, chorion and placenta

• after 13 days (rare): conjoined twins

Diagnosis of chorionicity and amnionicity

• in first trimester, high accuracy rates for chorionicity and amnionicity: determined by number of gestational sacs present, number of fetal heart beats or crown rump length (CRL) seen, or number of yolk sacs or amnions seen
• in second trimester, less accurate: determined by gender, number of placentas, dividing membrane, membrane thickness, presence or absence of the ‘twin peak sign’

Prenatal diagnosis

• must know chorionicity
• monozygotic pregnancies have similar risk to singleton pregnancies: one risk for the pregnancy

• rare: postzygotic non-disjunction

• dizygotic pregnancies

• each fetus has individual risk

• first trimester screening applicable with or without the biochemistry
• second trimester screening inaccurate as analytes are increased due to number of fetuses
• invasive testing: chorionic villus sampling and amniocentesis
• multifetal reduction in specialised centres for anomalies or reduction of fetal numbers

Complications of twin pregnancy

General

• increased miscarriage rate: vanishing twin
• increased perinatal mortality rate: five to seven times of singleton pregnancies

• death of one DCDA twin associated with preterm delivery
• death of one MC twin has risk of hypotensive blood transfusion and 25% risk of neurological damage to the surviving twin

• fetal abnormalities: higher incidence of cardiac and central nervous system malformations
• intrauterine growth restriction (IUGR)
• premature delivery: in up to 45% of twins, compared with 5%–6% of singleton births
• postpartum haemorrhage
• pre-eclampsia: three to five times the risk associated with singleton births; tends to be more severe

Specific: monochorionic twinning

Twin-to-twin transfusion syndrome (TTTS)

• 15% incidence
• requires arterial to venous anastomosis, which is unbalanced, and one of the fetuses, the donor, starts to transfuse the other twin, the recipient
• associated with velamentous cord insertion

Staging (Quintero)

• stage 1: polyhydramnios (deepest vertical pocket of amniotic fluid >8 cm) in one twin and oligohydramnios (deepest vertical pocket of amniotic fluid <2 cm) in the other with bladder seen in the donor
• stage 2: polyhydramnios and oligohydramnios present with no bladder seen in the donor
• stage 3: abnormal Dopplers

• donor: absent end diastolic flow or reversed in the umbilical artery
• recipient: abnormal venous Dopplers

• stage 4: fetal hydrops
• stage 5: fetal demise of one or both twins

Management

• termination of pregnancy
• conservative: 90% mortality rate
• cord occlusion/ligation
• serial amnioreduction
• laser coagulopathy: best treatment outcome with decreased morbidity

Selective intrauterine growth restriction (sIUGR)

• 15% incidence
• one twin is small for gestational age where the other twin is growing normally
• associated with increased risk of fetal demise and risk of neurological sequelae
• three classifications

Twin reversed arterial perfusion sequence (TRAP) or acardiac twinning

• 1% of monozygotic pregnancies
• associated with chromosomal abnormalities, arterial to arterial anastomosis
• leads to major deformities/fetal demise in the recipient twin and possible heart failure in the donor twin

Antenatal management of twin pregnancy

Diagnosis

• Multiple pregnancy is a differential diagnosis if the fundal height is greater than dates and is associated with hyperemesis.
• Diagnosis is confirmed by ultrasound scan.

Antenatal care

• More frequent visits are advisable because of raised maternal and fetal risks.
• Weekly visits between antenatal visits and ultrasound assessment from about 30 weeks gestation are appropriate. Advise regarding employment, rest and iron supplementation.

Ultrasound role

• determining zygosity
• look for fetal abnormality
• assess growth and wellbeing: increased fetal surveillance with serial scans
• treatment: laser therapy

Prevention of premature labour

• Twins are five times more likely to be preterm than singletons.
• Delivery prior to 32 weeks is more likely with monochorionic twins.
• No studies have shown that routine hospitalisation, cervical suture or tocolysis increase pregnancy length.

Delivery of twins

• In 70% of cases, the first twin is a cephalic presentation, and both twins are cephalic in 40%.
• Common practice is delivery at 37–38 weeks, as there is increased risk of stillbirth.

Indications for elective caesarean section

• malpresentation of the first twin
• monoamniotic twins
• other obstetric indications, such as placenta praevia

Vaginal delivery

• Vaginal delivery is probably appropriate for cephalic/cephalic presentation with normal growth and wellbeing.
• Evidence is unclear on method of delivery when the second twin is breech.
• Both twins are continuously monitored during labour.
• Epidural anaesthesia is recommended.
• Augmentation and induction of labour is acceptable in the absence of any obstetric contraindications.
• The third stage requires active management because of the risk of postpartum haemorrhage.

Twin with single intrauterine fetal death

The incidence of antepartum death of one twin is 3%–4%. The outcome of the surviving twin is related to whether the twins are monochorionic or dichorionic. In monochorionic twins there is a high rate of vascular communication between the twins and a risk of significant twin-to-twin transfusion. Neurological abnormalities in the surviving twin result from thromboplastins released from the dead fetus, which can cause thrombotic occlusion of cerebral vessels. Fetal magnetic resonance imaging (MRI) is helpful.

Triplet pregnancy

Incidence. Triplet pregnancies have a wide geographical variation, with an increased incidence in Africa. In Western countries, the incidence is 1 in 6400. For clomiphene-induced pregnancies, the incidence is 5 in 1000 and for assisted reproductive techniques 3%–4%.

Complications of triplet pregnancy

• maternal: anaemia, pre-eclampsia, antepartum haemorrhage
• fetal: premature labour, with up to 80% delivering before 37 weeks gestation; IUGR; malpresentation; increased perinatal mortality rate (five times that of singleton)
• reduction to twin or singleton pregnancy reduces morbidity and mortality rates

Delivery

The perinatal mortality rate rises as the time interval between deliveries lengthens. This may be due to progressive fetal anoxia with changes in uteroplacental haemodynamics. As a result, caesarean section is indicated. The risk of postpartum haemorrhage is heightened.

Further reading

Evans M.I., Ciorica D., Britt D.W., Fletcher J.C. Update on selective reduction. Prenatal Diagnosis. 2005;25:807-813.

Gratacos E., Lewi L., Munoz B., et al. A classification system for selective intrauterine growth restriction in monochorionic pregnancies according to umbilical artery Doppler flow in the smaller twin. Ultrasound in Obstetrics and Gynecology. 2007;30:28-34.

Pharoah P.O.D., Adi Y. Consequences of in utero death in a twin pregnancy. Lancet. 2000;355:1597-1602.

Quintero R.A., Morales W.J., Allen M.H., et al. Staging of twin–twin transfusion syndrome. Journal of Perinatology. 1999;19(8):550-555.

Roberts D., Gates S., Kilby M., Neilson J.P. Interventions for twin–twin transfusion syndrome: a Cochrane review. Ultrasound in Obstetrics and Gynecology. 2008;31:701-711.

Senat M.-V., Deprest J., Boulvain M., et al. Endoscopic laser surgery versus serial amnioreduction for severe twin-to-twin transfusion syndrome. New England Journal of Medicine. 2004;351:136-144.

Wald N.J., Rish S. Prenatal screening for Down syndrome and neural tube defects in twin pregnancies. Prenatal Diagnosis. 2005;25:740-745.

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