OP29.06: Mid-second trimester abdominal circumference ratio in a twin gestation predicts poor perinatal outcome

Abstract

The abdominal circumference (AC) ratio has been known to be a good predictor of birthweight discordance in twin pregnancy. The aim of this study was to evaluate the feasibility of the mid-second trimester AC ratio in predicting poor perinatal outcomes of twin gestations. The study population consisted of 150 consecutive twin pairs that were delivered between Jan 2004 and Jun 2007. Pregnancies complicated by intrauterine death or congenital anomaly were excluded. AC ratios were measured between 19–25 weeks' gestation. Birth weight discordance was defined as ≥ 25% difference in birth weight, relative to the larger twin. Receiver operating curve analysis was used to select a cut-off of the AC ratio for prediction of birthweight discordance. Perinatal outcome was compared between patients with a decreased AC ratio (an increased AC difference) and those with a normal AC ratio. 1) Mid-second trimester prediction of birth weight discordance in a twin pair, using an AC ratio with a cut off of 0.91, had a sensitivity of 67%, specificity of 89%, positive predictive value of 50% and negative predictive value of 94%. 2) Women with an AC ratio < 0.91 had a significantly higher rate of preterm birth < 34 weeks' gestation, birthweight discordance, small for gestational age (SGA) of one or both neonates in a pair than did those with an AC ratio ≥ 0.91 (preterm birth < 34 weeks of gestation: 32% vs 12%, P < .05; birth weight discordance: 50% vs 6%, P < .001; SGA: 31% vs 12%, P < .05). 3) Neonates with an AC ratio < 0.91 had a significantly higher rates of mechanical ventilator use, duration of NICU care > 30 days and neonatal death than those with an AC ratio ≥ 0.91 (mechanical ventilator use: 28% vs 13%, P < .05; duration of NICU care > 30 days: 18% vs 6%, P < .01; neonatal death: 13% vs 3%, P < .01). Abdominal circumference ratio < 0.91 in mid-second trimester was a good predictor of poor perinatal outcome in twin gestations.