Multiple pregnancy

Published on 09/03/2015 by admin

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Last modified 09/03/2015

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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)
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