Congenital Malformations And Season Of Birth: A Brief Review

Following is an abstract of a report by John C. Bailar, III, and Joan Gurian, of the National Cancer Institute, which appeared in Eugenics Quarterly, Vol. 12, No. 3, September 1965.

Several recent reports have revealed a correlation between congenital malformations and maternal disease. Since infectious diseases, as well as many other teratogenic factors, have seasonal patterns, the study of correlations between birth date and incidence of congenital malformations is obviously warranted. These correlations may be due to the direct influence of the disease, to medication taken, or to other external factors affecting either the mother or the fetus.

Most of the recent studies have concentrated on malformations of the musculoskeletal, the central nervous, and the cardiovascular systems. In one study (Hewitt, 1962) of 65 children with congenital malformations of the musculoskeletal system (excluding clubfoot), 48 were found to have been born during the months of July through December.

Most studies of congenital hip dislocation reveal a marked and distinct excess of winter births. In one, for example (Edwards, 1961), the incidence of this condition in January births was 2.03 times that found in the lowest month (unspecified).

An analysis of some 9,951 cases of congenital malformations of all kinds in the United Kingdom and Eire (Slater, Watson, and McDonald, 1964) also indicated an excess of congenital hip dislocations in the winter months as well as a similar excess for spina bifida. Malformed or partially absent limbs, however, were in excess among summer births. All malformations combined showed no seasonal cycle. On the other hand, Hewitt's study revealed that the number of malformed children born in New York City in December 1962 was above expectation. A third study (Stevenson, Worcester, and Rice, 1950) found no overall seasonal pattern, but noted a possible increase in the third quarter of the year in multiple defects, presumably developed during the second and third months of gestation.

Although the causes of such seasonal differences are unknown, most observers have tended to link them--with limited success--to monthly variations in maternal infections during early pregnancy. Other possible factors are seasonal variations in maternal nutrition or in conception rates among persons with relevant physical or genetic conditions. The recent experience with thalidomide has pointed up the need to search for drugs or other materials a pregnant woman might take more often in one season than another. (29 References)