A study of seasonal incidence of congenital malformations in the United States.

Seasonal variation in the incidence of isolated cleft lip cleft lip and palate anencephaly spina bifida hydrocephaly congenital heart disease anorectal defects hypospadias positional foot defects polydactyly snydactyly reduction deformities and Downs syndrome was investigated using data generated through the National Cleft Lip and Palate Intelligence Service (NIS) for 1962-1965. Only cleft lip with or without cleft palate hypospadias and positional foot defects showed a statistically seasonal trend. Cleft lip/palate showed a seasonal trend for the entire NIS region (U.S.) but only the area with a hot summer and a moderate winter showed a significant climatic trend with a peak incidence in January 2 months earlier than the national trend. Hypospadias had a maximum incidence in April for the entire area with a seasonal variation in the moderate summer-moderate winter regions. The national incidence of positional foot defects was greatest in March. A similar trend was noted in the hot summer-cold winter region.