The ninety-fifth percentile for growth discordance predicts complications of twin pregnancy.

Abstract

Our purpose was to define twin growth discordance on the basis of perinatal outcome. Twins delivered at >23 weeks' gestation between 1995 and 2000 were identified by use of our computerized perinatal database. Birth weight (BW), chorionicity, and the following outcomes were recorded: cesarean delivery for nonreassuring fetal status (NRFS), umbilical artery (UA) pH, 5-minute Apgar score, neonatal intensive care unit (NICU) admission, and stillbirth. Discordance was calculated as 100 x(Larger BW - Smaller BW)/Larger BW. The distribution of discordance values for the study population was determined. Outcomes were compared for twins with and without discordance at thresholds defined by population percentile. The mean discordance for 346 twins was 11.4% +/- 10.5%. The 75th percentile was 16% discordance, the 90th was 23%, and the 95th was 31%. Discordance was independently associated with outcomes. The 95th percentile was the threshold most predictive of cesarean section NRFS, UA pH <7.1, 5-minute Apgar score <7, and NICU admission. Defining pathologic discordance as the 95th percentile, or >30% difference, enhances its predictive value.