Second-Trimester Estimated Fetal Weight and Discordance in Twin Pregnancies

OBJECTIVES: The purpose of this study was to estimate the association between second-trimester estimated fetal weight and fetal growth restriction in twin pregnancies. METHODS: A historical cohort of 306 twin pregnancies from a single center was analyzed. Estimated fetal weight and discordance at 18 to 24 weeks were calculated. Patients with a fetus whose second-trimester estimated fetal weight was below the 10th percentile were compared to patients with both fetuses at or above the 10th percentile. Also, patients with second-trimester discordance of 15% or greater were compared to patients with discordance of less than 15%. RESULTS: Second-trimester discordance was significantly smaller than birth weight discordance (mean discordance ± SD, 7.41% ± 6.06% versus 11.43% ± 9.6%, respectively; P < .001). Patients with second-trimester discordance of 15% or greater were significantly more likely to deliver a twin with a birth weight below the 10th percentile for gestational age (67.7% versus 44.1%; P = .012) and below the 5th percentile for gestational age (41.9% versus 22.8%; P = .019). Patients with a second-trimester estimated fetal weight below the 10th percentile were significantly more likely to deliver a twin with a birth weight below the 10th percentile for gestational age (65.5% versus 44.5%; P = .031) and below the 5th percentile for gestational age (55.2% versus 21.5%; P < .001). CONCLUSIONS: In twin pregnancies, second-trimester estimated fetal weight below the 10th percentile and discordance of 15% or greater are associated with fetal growth restriction.