Intrauterine growth of twins in Taiwan.

During the period between January 1, 1980 and December 31, 1991, there was a total of 21,348 live born neonates delivered in our hospital. Among them, there were 368 pairs of twins and 18 sets of triplets. The incidences of twin and triplet pregnancy were 1.76% (one pair in every 57.8 live deliveries) and 0.086% (one set in every 1,164 live deliveries), respectively. The mode of gestational age for all twins in this study was 36.6 +/- 3.2 weeks (36.6 +/- 3.6 weeks for vaginal delivery and 36.7 +/- 2.8 weeks for cesarean section, respectively). Among twins delivered by cesarean section, the birth weight of the first born twin was significantly heavier than the second born twin; however, this difference was not observed for those twins delivered vaginally. Also, the birth weight between male and female was not significantly different. However, for those twin pairs of different sexes, the birth weight for the male twin was significantly heavier than the female co-twin. In those cases the mean birth weight increased steadily as the gestational age increased and plateaued at about the 40th week. Compared to the intrauterine growth curve of the Chinese singleton, the difference started from the 33rd gestational week and reached a significant level at about the 37th gestational week. This may indicate the incipient of the placental insufficiency for multiple pregnancies. The intrauterine growth curve for twin pregnancies may serve as guide for studying the mortality and morbidity of twins in the future.