Monochorionic Diamniotic Twin Pregnancy

Monochorionic diamniotic twin pregnancy is a twin pregnancy with one shared placenta and two amniotic sacs, from division of the embryo between days 4 and 8 after fertilisation. It is always identical. It matters because the shared placenta contains vascular connections, so twin to twin transfusion syndrome, twin anaemia polycythaemia sequence and selective growth restriction can develop, with higher fetal loss than dichorionic twins.

• Risk factors: assisted conception, identical twinning.
• Chorionicity is found by the T sign at 11 to 13 weeks.
• Surveillance every 2 weeks from 16 weeks finds complications early.

Women have a uterus larger than dates and symptoms of multiple pregnancy. Rapidly increasing abdominal size over 1 to 2 weeks, breathlessness or discomfort suggest twin to twin transfusion with polyhydramnios.

• Rapid increase in fundal height.
• Different liquor volumes in the two sacs.
• Differential diagnosis: dichorionic twins, twin to twin transfusion syndrome, selective growth restriction, twin anaemia polycythaemia sequence, polyhydramnios from other cause, conjoined twins.
• Complications: twin to twin transfusion syndrome, twin anaemia polycythaemia sequence, selective growth restriction, single fetal death with injury to the co-twin, preterm birth, preeclampsia, structural anomaly in one twin, stillbirth.

The approach is an ultrasound schedule from 16 weeks.

• Ultrasound at 11 to 13 weeks: T sign (thin membrane meeting the placenta at a right angle); crown rump length and nuchal translucency in both twins.
• Every 2 weeks from 16 to 24 weeks: deepest vertical pocket in each sac, fetal bladders, umbilical artery Doppler, estimated fetal weight; growth discordance above 20 percent needs action.
• Twin to twin transfusion syndrome: recipient deepest pocket 8 cm or more (10 cm or more after 20 weeks) and donor deepest pocket 2 cm or less; staging by bladder appearance, Doppler and heart changes.
• Middle cerebral artery peak systolic velocity every 2 weeks from 20 weeks for twin anaemia polycythaemia sequence; fetal echocardiography at 20 to 22 weeks; growth scans every 2 weeks.

The principle is fortnightly ultrasound, treatment of transfusion syndrome by laser, and delivery at 36 weeks.

• Supportive: antenatal review every 2 weeks from 16 weeks; early warning on rapid abdominal growth, contractions and leaking fluid; high energy diet; birth in a facility with caesarean section and neonatal intensive care.
• Pharmacological: folic acid 400 micrograms oral daily; ferrous sulphate 200 mg oral once daily (8-hourly if anaemic); 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; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks; nifedipine 20 mg oral once then 10 to 20 mg every 6 to 8 hours for up to 48 hours for contractions; 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: fetoscopic laser coagulation of the placental connections at 16 to 26 weeks for twin to twin transfusion stage II or above, or stage I with worsening; amnioreduction of up to 2 litres, no faster than 1 litre per 20 minutes, when laser is not available; delivery at 36 weeks and 0 days to 36 weeks and 6 days, earlier for complications; vaginal birth if the first twin is cephalic, otherwise caesarean section.
• Special groups: monochorionic monoamniotic twins (one shared sac) have admission and daily monitoring from 26 to 28 weeks and caesarean section at 32 to 34 weeks because of cord entanglement.
• Red flags: rapid abdominal growth, discordant liquor, discordant growth above 20 percent, absent end diastolic flow, fetal death of one twin, contractions, leaking fluid.
• Follow-up: scans every 2 weeks to delivery; newborn haemoglobin and cranial ultrasound if there was a complication; postnatal haemoglobin at 24 hours.