Multiple Pregnancy

Pregnancy with two or more fetuses, classified by zygosity and chorionicity, the latter being the single most important determinant of risk and management pathway.

Dichorionic diamniotic (DCDA) twins (either dizygotic, or monozygotic splitting within 3 days of fertilization) have separate placentas and carry the lowest risk.

Monochorionic diamniotic (MCDA) twins (monozygotic splitting 4 to 8 days post-fertilization) share a single placenta with a shared circulation, carrying specific risks including twin-to-twin transfusion syndrome.

Monochorionic monoamniotic (MCMA) twins (splitting after day 8) share both placenta and amniotic sac, carrying the highest risk given the potential for cord entanglement.

Uterine size greater than expected for dates, exaggerated pregnancy symptoms (nausea, breathlessness), and, later in pregnancy, palpation of multiple fetal poles.

Multiple pregnancy carries substantially elevated risk of nearly every obstetric complication: hyperemesis, pre-eclampsia, gestational diabetes, anemia, preterm labor (the leading cause of perinatal morbidity in twins), malpresentation, and postpartum hemorrhage.

• Chorionicity must be determined by ultrasound in the first trimester (ideally 11 to 14 weeks), since it becomes progressively harder to assess later and dictates the entire subsequent management pathway; the lambda sign (a triangular projection of placental tissue between the membranes at the base) indicates dichorionicity, while the T-sign (membranes meeting the placenta at a right angle) indicates monochorionicity
• Serial growth scans are more frequent than in singleton pregnancy: every 4 weeks from 20 weeks in DCDA twins, every 2 weeks from 16 weeks in MCDA twins, given the need for early detection of twin-to-twin transfusion syndrome
• Screening for twin-to-twin transfusion syndrome in monochorionic twins uses ultrasound assessment of amniotic fluid discordance (oligohydramnios in one sac, polyhydramnios in the other) and bladder visualization, staged using the Quintero staging system

• Aspirin 75 to 150 mg PO od from 12 weeks, given multiple pregnancy is itself a risk factor for pre-eclampsia
• Increased iron and folate supplementation given elevated anemia risk
• Twin-to-twin transfusion syndrome (MCDA twins): significant or progressive disease (Quintero stage II or above) is treated with fetoscopic laser ablation of the shared placental vascular anastomoses at a specialist fetal medicine center, offering the best outcomes compared with amnioreduction alone
• Timing of delivery: uncomplicated DCDA twins, offer delivery from 37 to 37+6 weeks; uncomplicated MCDA twins, offer delivery from 36 to 37 weeks (after a course of corticosteroids given the earlier timing); MCMA twins are typically delivered by planned cesarean around 32 to 34 weeks, given the ongoing cord entanglement risk, often with prior admission for continuous monitoring from around 26 to 28 weeks
• Mode of delivery: vaginal delivery is generally appropriate if the first (presenting) twin is cephalic, with cesarean considered for a non-cephalic first twin, MCMA twins, or other specific complications; delivery of twins should occur in a unit with immediate access to cesarean facilities given the risk of complications with the second twin
• Active management of the third stage is essential given substantially elevated postpartum hemorrhage risk from uterine overdistension, with oxytocin infusion often continued for a longer duration postpartum

Referral: obstetric-led care for all multiple pregnancies; specialist fetal medicine center for monochorionic twins and any suspected twin-to-twin transfusion syndrome.