Dichorionic Diamniotic Twin Pregnancy

Dichorionic diamniotic twin pregnancy is a twin pregnancy in which each twin has its own placenta and its own amniotic sac. It is the commonest type of twin pregnancy, and includes all non identical (dizygotic) twins and some identical twins that split in the first 3 days after fertilisation. It matters because the risks of preterm birth, preeclampsia, anaemia, gestational diabetes, growth restriction and postpartum haemorrhage are higher than in a singleton, but the risks specific to shared placentas are absent.

• Risk factors: assisted conception, maternal age above 35 years, family history, high parity, African ancestry.
• Birth often occurs before term.
• Chorionicity is best defined by ultrasound at 11 to 13 weeks, with the lambda sign.

Women have a uterus larger than dates, more marked nausea, fatigue, breathlessness, swelling and backache. Two fetal heart rates may be found.

• Fundal height 3 or more cm above dates by 20 to 24 weeks.
• Raised maternal serum alpha fetoprotein and human chorionic gonadotrophin.
• Differential diagnosis: wrong dates, polyhydramnios, large single fetus, fibroids, molar pregnancy, ovarian mass.
• Complications: preterm labour, preeclampsia, anaemia, gestational diabetes, growth restriction, discordant growth, malpresentation, postpartum haemorrhage, stillbirth.

The approach is early ultrasound to confirm chorionicity and a schedule of scans.

• Ultrasound at 11 to 13 weeks: two separate placentas or a thick membrane with the lambda (twin peak) sign defines dichorionic diamniotic twins; label the twins by position.
• Detailed anomaly scan at 18 to 22 weeks; cervical length at 20 to 24 weeks; growth scans every 4 weeks from 24 weeks.
• Full blood count at booking, 20 weeks and 28 weeks; 75 g oral glucose tolerance test at 24 to 28 weeks; blood pressure and urine protein at each visit.
• Where ultrasound is unavailable, use clinical examination, refer for scan at 20 weeks and plan birth in a hospital.

The principle is antenatal care with more frequent review, prevention of preeclampsia and anaemia, and delivery at 37 weeks.

• Supportive: antenatal review every 4 weeks to 28 weeks, then every 2 weeks; high energy diet (increase by 300 kcal daily); rest; early warning on preterm labour symptoms; birth in a facility with caesarean section and neonatal care.
• Pharmacological: folic acid 400 micrograms oral daily through pregnancy; ferrous sulphate 200 mg oral once daily as prophylaxis (8-hourly if haemoglobin is below 11 g/dL); aspirin 150 mg oral at night from 12 weeks to 36 weeks; calcium 1.5 g elemental oral daily where intake is low; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if preterm birth is likely; oxytocin 10 IU IM at birth then infusion of 20 IU in 1 litre sodium chloride 0.9 percent at 125 mL per hour for 4 hours.
• Procedures: planned birth at 37 weeks; vaginal birth if the first twin is cephalic, with continuous cardiotocography and an obstetrician and neonatal team present; caesarean section if the first twin is not cephalic or for obstetric indications; no routine cerclage or pessary.
• Red flags: contractions, leaking fluid, bleeding, blood pressure 140/90 mmHg or more, reduced fetal movements, growth difference above 20 percent.
• Follow-up: growth scans every 4 weeks (every 2 weeks if discordant); postnatal haemoglobin at 24 hours; ferrous sulphate 200 mg oral 8-hourly for 3 months if anaemic.