Selective Fetal Growth Restriction

Selective fetal growth restriction (sFGR) complicates about 10 to 15% of monochorionic twin pregnancies (and also dichorionic twins). It is defined by estimated fetal weight of one twin below the 10th centile (or below the 3rd percentile in some definitions) with an inter twin discordance of at least 25% (consensus: EFW below the 3rd centile, or at least two of AC below the 10th centile, EFW below the 10th centile, and discordance of at least 25%). It is caused by unequal placental sharing and anastomoses.

Gratacos classification for monochorionic twins, by the umbilical artery Doppler of the smaller twin:

• Type I: positive end diastolic flow (good prognosis; about 2 to 4% risk of unexpected fetal death, normal development in over 90%)
• Type II: persistently absent or reversed end diastolic flow (poor prognosis; high risk of deterioration and death of the smaller twin, 90% need delivery before 32 weeks; risk of neurological injury to the larger twin about 10 to 15%)
• Type III: intermittent absent or reversed end diastolic flow (cyclical; unpredictable sudden death of the smaller twin in 10 to 15%, with a risk of neurological damage to the larger twin of about 10 to 20% because of large arterio arterial anastomoses)

• Usually asymptomatic; discordant growth on ultrasound
• Oligohydramnios of the smaller twin; polyhydramnios of the larger twin may occur
• Risk of unpredictable intrauterine death of one twin (with acute transfusion causing death or neurological damage in the co-twin)
• Preterm birth, low birth weight, and neonatal complications

• Establish chorionicity in the first trimester
• Ultrasound every 2 weeks from 16 weeks in monochorionic twins; estimated fetal weight, discordance, amniotic fluid volumes, bladder visualisation, and Dopplers (umbilical artery, middle cerebral artery peak systolic velocity for TAPS, ductus venosus)
• Classify type I, II or III by umbilical artery Doppler pattern of the smaller twin
• Fetal echocardiography and anomaly scan; karyotyping or microarray for early onset growth restriction
• Exclude TTTS, TAPS, infection (CMV, toxoplasma), and structural anomalies

• Type I: expectant with weekly or fortnightly ultrasound and Doppler; deliver at 34 to 36 weeks (up to 37 weeks).
• Type II: individualised; weekly surveillance with ductus venosus and umbilical artery Doppler, and cardiotocography (computerised) in the smaller twin; deliver at about 30 to 32 weeks (earlier for ductus venosus changes, reversed a-wave, or abnormal cardiotocography), with antenatal corticosteroids (betamethasone 12 mg IM, two doses 24 hours apart) and magnesium sulfate for neuroprotection below 32 weeks (4 g IV loading then 1 g/hour).
• Type III: close surveillance; deliver at about 32 to 34 weeks.
• Fetal therapy in selected severe cases at 16 to 26 weeks: selective feticide of the smaller twin by radiofrequency ablation or cord occlusion (to protect the larger twin; survival of the larger twin about 85 to 90%), or fetoscopic laser coagulation of placental anastomoses (survival of at least one twin about 85 to 90%, risk of death of the smaller twin about 40 to 60%).
• Delivery by caesarean or vaginal delivery in a centre with neonatal intensive care.
• Counselling regarding risk of death of one twin and neurological impairment of the co-twin, and possible later neuroimaging (MRI of survivors).