RESUMO
Background: A higher prevalence of congenital malformations among twins than among single has been reported in the literature. Aim: To study the incidence of congenital malformations in twins in the maternity hospital of the University of Chile in the period 1983-1997. Material and methods: As part of the Latin American Collaborative Study of Congenital Malformations, every newborn in the maternity hospital was examined by a neonatologist and congenital malformations were recorded in a special file. Results: In the study period there were 48.663 deliveries of single pregnancies and 448 deliveries of twin pregnancies, giving birth to 886 twins borns alive and 17 stillbirths (1.9 percent mortality). Of these, there were 423 twins, 17 triplets, a sextuple delivery and two siamese. Seven point one percent of twins born alive and 6.5 percent of single newborns had a congenital malformation. The prevalence of malformations in twins and single stillbirths was 35.2 and 17.2 percent respectively (p <0.04). In four pairs and siamese newborns, malformations typical of monozygotic twins were present, such as an acardiac fetus with Trap sequence, a papyraceous fetus and two with hydroanencephaly. Twelve twins had malformations attributable to uterine compression. Conclusions: This study did not find a higher frequency of malformations comparing twins with single babies born alive, but in stillbirths there was a significant difference between single and twin stillbirths (7.1 percent versus 35.2 percent, respectively, p <0.05)