A case-control study of 1253 twin pregnancies from a 1982-1987 perinatal data base.

In one regional perinatal network between 1982-1987, 101,506 women delivered infants greater than 500 g, of which 1253 were twin pregnancies (1.2%). This latter group was compared statistically with a 5% random sample of the singletons (N = 5119). The results showed that the women with twin pregnancies were slightly older, had a higher parity, gained more weight during the gestation, and had a heavier body weight at delivery. Twin pregnancies were complicated by increases in hypertension (odds ratio 2.5; 95% confidence interval 2.1-3.1), abruption (odds ratio 3.0; 95% confidence interval 1.9-4.7), and anemia (odds ratio 2.4; 95% confidence interval 1.9-3.0). There was no increased risk of pyelonephritis, placenta previa, or diabetes mellitus in mothers with twins. The twin pregnancies delivered earlier and the infants were smaller, had lower Apgar scores, and were at increased risk for congenital anomalies. Fetal and neonatal mortality rates were significantly increased in the twin infants; the perinatal mortality rates for twin A and twin B were 48.8 and 64.1, respectively, compared with 10.4 per 1000 births for the singleton controls. When the twin infants A and B were of similar weight, they had a similar perinatal mortality (odds ratio 1.0; 95% confidence interval 0.6-1.8). For infants less than 2500 g, twins A and B had lower fetal and neonatal mortality rates than did singletons, but twins heavier than 2500 g were at increased risk of perinatal death.