Sonographically thick placenta: a marker for increased perinatal risk--a prospective cross-sectional study.

The aim of this study was to determine placental thickness by ultrasound examination throughout pregnancy and establish the correlation of sonographically thick placenta with perinatal mortality and morbidity. Placental thickness was determined by routine sonographic examination throughout pregnancy in 561 normal singleton pregnancies. Thick placenta was determined as placenta that was above the 90th percentile. Gravidae between 20-22 weeks' gestation (n=193) and 32-34 weeks (n=73) were then divided into two groups according to placental thickness. The study group consisted of 44 gravidae with thick placenta. The control group included 151 gravidae with placental thickness between the 10th and 90th percentile. A comparison of perinatal mortality and morbidity rates as well as the incidence of small and large for gestational age neonates was conducted.A linear increase of placental thickness was found to correlate with gestational age throughout pregnancy. No statistical differences were observed between the two groups with regard to obstetrical variables such as maternal age, parity and gestational age at delivery. No correlation was found between placental thickness and maternal age or parity. The incidence of perinatal mortality was significantly higher among gravidae with thick placentae (6.82% versus 0.66 per cent, P=0.037, 95 per cent confidence interval 1.71-70.29). Birthweight at term was found to be above 4000 g in 20.45 per cent of the thick-placenta group as compared to 5.3 per cent in the control group (P=0.001, 95 per cent CI 2.08-13.85), and birthweight of less than 2500 g was found in 15. 9 per cent of the thick-placenta group as compared to 7.3 per cent in the control group (P=0.03, 95 per cent CI 1.11-8.14). The incidence of fetal anomalies was 9.1 per cent in the thick-placenta group and 3.97 per cent in the control group (not significant). Sonographically thick placenta is associated with increased perinatal risk with increased mortality related to fetal anomalies and higher rates of both small for gestational age and large for gestational age infants at term. Copyright 2000 Harcourt Publishers Ltd.