Factors affecting risks of congenital malformations. I. Analysis of epidemiologic factors in congenital malformations. Report from the Collaborative Perinatal Project.

An analysis was made of over 30 demographic, biologic and medical variables in relation to risks of congenital malformations which occurred in the Collaborative Perinatal Project. The study population consisted of 46,689 single and multiple live births and fetal deaths about whom complete information was available on all study variables. Included in the analysis were 5 general malformation categories, 27 specific major, and 7 specific minor malformations. Several new associations were detected between epidemiologic factors and risks of specific malformations while other previously reported associations were confirmed by the present investigation. The analysis of general categories of malformations showed that multiple births had a higher frequency of major malformations than single births; whenever sex differences in incidence were noted, males, with few exceptions, had an excess of malformations over females; and maternal diabetes during pregnancy was associated with increased risk of major malformations in the fetus. Among specific findings of possible etiologic significance were that the risk for microcephaly was associated with infrequent prenatal visits and the presence of maternal hyperthyroidism; and unusually low weight gain and infrequent prenatal visits were associated with increased risk for lung hypoplasia. There was no significant effect of inbreeding of the fetus or mother on the risks of general or specific types of malformations. Anencephaly was more frequent among white than among Negro infants, whereas no difference in incidence was noted in spina bifida between the two racial groups. This finding points to an inconsistency in the hypothesis of common etiology for these malformations. Whites were also found to have significantly higher incidences over Negroes of pyloric stenosis, congenital dislocation of the hip, micrognathia, and pectus excavatum, while Negroes have higher incidences of metatarsus varus and inguinal hernia.