Multiple Pregnancy

Question 1

What are the types of twin pregnancy and how are they determined?

Answer 1

1. Dichorionic Diamniotic (DCDA)- 2 placentas, 2 membranes - Lambda/twin peak sign on USS <14 weeks
2. Monochorionic Diamniotic (MCDA) - 1 placenta, 2 membranes, T-sign on USS <14 weeks
3. Monochorionic Monoamniotic (MCMA), 1 placenta, no membranes- No dividing membrane; cord entanglement risk

Chorionicity should be determined at first-trimester scan — this is the most important prognostic factor.

Question 2

Why is chorionicity important?

Answer 2

Monochorionic twins share a placenta → risk of:

Twin-to-twin transfusion syndrome (TTTS) — MCDA only (15-20% risk)
Unequal placental sharing → selective FGR
Twin anaemia polycythaemia sequence (TAPS)
Co-twin death/neurological injury if one twin dies (shared circulation)
Higher rates of preterm birth, FGR
MCMA has additional risk of cord entanglement

Question 3

What is the monitoring schedule for twin pregnancies?

Answer 3

DCDA: USS every 4 weeks from 24 weeks
MCDA: USS every 2 weeks from 16 weeks (for TTTS)
MCMA: Intensive monitoring; often admitted from 24-26 weeks with daily CTG; delivery by 32-34 weeks

Question 4

When should twins be delivered?

Answer 4

DCDA- 37+0
MCDA - 36+0
MCMA - 32+0 to 33+6 weeks (by CS)
Triplets - 35 weeks

Question 5

What is twin-to-twin transfusion syndrome (TTTS)?

Answer 5

Occurs in MCDA twins only
Unbalanced blood flow through placental anastomoses
Donor twin: Anaemic, growth restricted, oligohydramnios (stuck twin)
Recipient twin: Polycythaemic, macrosomic, polyhydramnios, cardiac overload, hydrops
Staged using Quintero staging (I-V)
Treatment: Fetoscopic laser ablation of placental anastomoses (at fetal medicine centre)
Without treatment: high mortality (~90%)