A 30-year-old woman at 32 weeks with twin pregnancy (dichorionic-diamniotic twins) is noted on routine ultrasound to have estimated fetal weight discordance: Twin A 1,650 g (on the 15th centile) and Twin B 1,200 g (below the 3rd centile). What percentage discordance threshold is used to define significant twin growth discordance?
- A >25% ✓
- B >10%
- C >20%
- D >30%
Correct answer: A. >25%
Explanation
Twin growth discordance is calculated as: [(larger EFW − smaller EFW) / larger EFW] × 100. Discordance >25% is the widely used threshold (SMFM 2019, ISUOG guidelines) for clinically significant growth discordance in twin pregnancies, associated with increased risk of perinatal mortality and morbidity. In this case: (1650 − 1200)/1650 × 100 = 450/1650 × 100 = 27.3%, which exceeds the 25% threshold and warrants enhanced surveillance with Doppler velocimetry.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.