Discordance for Defects in Monochorionic Twins: Prevalence and Impact on Perinatal Outcomes

Area of Science:

• Perinatology
• Maternal-Fetal Medicine
• Genetics

Background:

• Monochorionic (MC) twins have a higher risk of congenital abnormalities than singletons.
• Discordance for structural defects occurs in 80% of affected twin pregnancies.
• Normal comparative genomic hybridization (aCGH) results do not exclude structural anomalies in MC twins.

Purpose of the Study:

• To determine the prevalence of discordant structural defects in MC twins with normal aCGH.
• To identify common defect types and their association with perinatal outcomes.
• To assess risks of fetal loss and preterm birth in these pregnancies.

Main Methods:

• Retrospective analysis of 381 MC twin pregnancies with first-trimester screening.
• Inclusion criteria: discordant structural fetal anomalies and normal aCGH.
• Data collection on defect types, fetal loss, preterm birth, and associated factors.

Main Results:

• 21 (5.5%) MC twin pregnancies had discordant structural defects with normal aCGH.
• Most common defects: cardiac (8), central nervous system (CNS) (6), and facial (3).
• Intertwin crown-rump length (CRL) discordance >20% correlated with fetal demise (p=0.046).
• Preterm birth before 32 weeks (47%) strongly associated with polyhydramnios (p=0.001), especially in CNS/facial defects.

Conclusions:

• Approximately 5% of MC twins exhibit discordant structural defects despite normal aCGH.
• Cardiac anomalies are the most frequent type of discordant defect.
• Intertwin CRL discordance >20% is a significant risk factor for fetal loss in MC twins.