Management of Significant Twin Growth Discordance (≥25%)

Definition and Epidemiology

Severe growth discordance is defined as an estimated fetal weight (EFW) difference of ≥ 25 % between twins and is linked to markedly higher fetal mortality and morbidity. 1, 2, 3
Discordance severity thresholds: mild ≥ 15 %, moderate ≥ 20 %, severe ≥ 25 % (calculated as the percentage difference in EFW). 1, 2
In monochorionic diamniotic pregnancies, isolated twin‑weight discordance ≥ 25 % occurs in approximately 11.6 % of cases. 1, 2

Monochorionic twins with any growth discordance should undergo umbilical artery Doppler velocimetry even in the absence of other complications, because abnormal Doppler patterns can appear as early as 16–20 weeks and predict adverse outcomes, including fetal demise. 1, 2
Umbilical artery Doppler has no proven benefit in uncomplicated dichorionic twins but becomes valuable when growth delay is suspected. 1, 2

Perform transabdominal ultrasound every 2–3 weeks to evaluate fetal growth, EFW percentiles, and abdominal circumference measurements. 1, 2
At each scan, assess amniotic‑fluid volume in each sac; oligohydramnios may signal twin‑twin transfusion syndrome in monochorionic twins or uteroplacental insufficiency in any chorionicity. 1, 2, 3
An abdominal‑circumference discordance > 10 % between 14–22 weeks is the strongest predictor of later adverse outcomes in both monochorionic and dichorionic pregnancies. 1, 2

Umbilical‑artery Doppler velocimetry is essential whenever growth discordance is identified, particularly in monochorionic twins. 1, 2
Absent or reversed end‑diastolic flow in the umbilical artery indicates severe placental insufficiency. 2, 3
Evaluate the ductus venosus for reversal of the A‑wave and assess for tricuspid regurgitation; these findings denote fetal cardiac compromise. 2, 3

Initiate non‑stress testing (NST) or biophysical profile (BPP) surveillance using the same criteria applied to singleton pregnancies with suspected growth restriction. 1, 2, 3
NST and BPP have comparable reliability in multiple gestations as in singletons for detecting fetal compromise. 1, 2
The American College of Obstetricians and Gynecologists recommends individualized management based on consensus and expert opinion, always considering the welfare of both fetuses. 1, 2

Screen for velamentous cord insertion and vasa previa, conditions that are more prevalent in twin gestations and can contribute to growth discordance. 4, 5
Perform transvaginal cervical‑length assessment to stratify the risk of preterm delivery. 4, 5
Offer fetal echocardiography in monochorionic twins because of a substantially increased risk of structural cardiac anomalies (approximately eight‑fold higher in monoamniotic twins and elevated in all monochorionic gestations). 4, 5

Specialist referral is advised in the first trimester when crown‑rump length (CRL) discrepancy is ≥10 % or nuchal translucency (NT) discordance is ≥20 % – early identification enables timely monitoring and intervention. 6
NT discordance ≥20 % occurs in ≈25 % of monochorionic twins and is associated with up to a 30 % risk of severe twin‑twin transfusion syndrome (TTTS) or early intra‑uterine fetal demise – highlights the prognostic value of NT measurement. 6
CRL discordance ≥10 % is significantly linked to pregnancy loss, with a pooled predictive risk of about 52 % – underscores the importance of precise early biometric assessment. 6
First‑trimester size disparity raises the likelihood of underlying growth restriction, chromosomal abnormalities, congenital anomalies, and subsequent fetal demise – warrants comprehensive evaluation for etiologic factors. 7

In monochorionic pregnancies, surveillance should commence at 16 weeks with fetal biometry every 2–3 weeks and weekly assessment for TTTS or other monochorionic complications – early Doppler and growth monitoring improve detection of adverse outcomes. 6

Standard singleton growth charts should be employed for twin biometry, recognizing that twin growth naturally decelerates relative to singletons – facilitates appropriate interpretation of percentile data. 6

Screening for velamentous cord insertion and vasa previa is recommended, as these anomalies are present in up to 22 % of monochorionic twins and are more prevalent across all twin gestations – early detection can guide delivery planning. 7
Transvaginal cervical‑length measurement at the routine anatomic survey (18–22 weeks) should be performed to stratify the risk of preterm delivery – a short cervix identifies candidates for prophylactic interventions. 6
Assessment for placenta previa is advised because its incidence is higher in twin pregnancies, particularly in dichorionic twins – informs obstetric management and delivery timing. 7

When growth restriction is identified, clinicians should consider viral infections and chromosomal abnormalities as potential causes, although unequal placental sharing remains the most common etiology – comprehensive work‑up ensures appropriate counseling and management. 6