A 32-year-old woman with a monochorionic diamniotic twin pregnancy is seen at 24 weeks for routine antenatal care. Ultrasound shows Twin A with an estimated fetal weight of 650 g and Twin B with 580 g. Doppler studies reveal absent end-diastolic velocity (AEDV) in the umbilical artery of Twin B, with normal Doppler in Twin A. The patient is asymptomatic with normal blood pressure and no proteinuria. What is the most appropriate next step in management?

Explanation

## Clinical Scenario This case presents a **monochorionic diamniotic twin pregnancy with selective intrauterine growth restriction (sIUGR) in Twin B**, evidenced by: - Significant weight discordance (>15%) - Absent end-diastolic velocity (AEDV) in umbilical artery of the growth-restricted twin - Monochorionic placentation (shared placenta, separate amniotic sacs) ## Pathophysiology of sIUGR in Monochorionic Twins **Key Point:** In monochorionic pregnancies, unequal placental sharing (one twin receives disproportionately less placental territory) leads to selective IUGR. The growth-restricted twin is at high risk of intrauterine death, especially with abnormal Doppler studies. **Mnemonic: AEDV = Absent End-Diastolic Velocity** — indicates severe placental insufficiency and fetal compromise; requires intensive monitoring and delivery planning. ## Management Strategy at 24 Weeks with AEDV ### Rationale for Twice-Weekly Monitoring 1. **Gestational age 24 weeks** — at the threshold of viability; delivery carries significant neonatal morbidity 2. **AEDV present** — indicates severe placental insufficiency but not yet reversed flow (AREDV) 3. **Twin A normal** — justifies prolonging pregnancy if Twin B can be monitored safely 4. **Monochorionic risk** — shared placenta means complications in one twin can affect the other; close surveillance is essential ### Monitoring Protocol - **Twice-weekly CTG** (cardiotocography) of both twins to assess fetal well-being - **Twice-weekly Doppler** — umbilical artery, middle cerebral artery (MCA), and ductus venosus - **Delivery triggers:** - Reversed flow in umbilical artery (AREDV) or ductus venosus - Absent/reversed flow in MCA - Non-reassuring CTG in either twin - Spontaneous labor or rupture of membranes - **Planned delivery at 32 weeks** (balance between neonatal survival and risk of intrauterine death) **Clinical Pearl:** The presence of AEDV (but not reversed flow) at 24 weeks in a monochorionic pregnancy allows for expectant management with intensive monitoring. Delivery at 32 weeks provides reasonable neonatal outcomes while reducing the risk of intrauterine fetal death in the growth-restricted twin. **High-Yield:** AEDV is a sign of severe but compensated placental insufficiency. Reversed diastolic flow (AREDV) or abnormal ductus venosus Doppler are indications for urgent delivery, even in the previable period, due to imminent fetal death risk. ## Why Not the Other Options? ### Immediate Delivery at 24 Weeks - Neonatal survival at 24 weeks is ~50%, with significant morbidity (IVH, BPD, NEC) - Twin A is appropriately grown with normal Doppler — no indication for iatrogenic prematurity - AEDV alone (without reversed flow) does not mandate immediate delivery ### Selective Feticide of Twin B - Selective feticide is considered when one twin has a lethal anomaly or severe complications incompatible with life - IUGR with AEDV is not an absolute indication; the twin may still survive with intensive monitoring - Feticide carries procedural risks and leaves Twin A as a singleton with monochorionic placental complications - Reserve for cases of severe anomaly or when expectant management has failed ### Monthly Ultrasound and Term Delivery - Monthly monitoring is **insufficient** for a monochorionic twin with AEDV - Risk of sudden intrauterine fetal death in Twin B is high; weekly or twice-weekly assessment is standard - Expectant management to term is not safe given the severity of placental insufficiency