The seasonal conception of lethal congenital malformations

Background. The objective of the study was to investigate the possibility of the effect of seasonal temperature on the incidence of lethal congenital malformations in a retrospective study. Methods. At the National Institute of Perinatology in Mexico City, perinatal deaths due to congenital malformations were compared with the the remainder of perinatal deaths over a period of 3 years in relation to the average temperature of the months in which the fifth week of gestation occurred. Results. The division between the average temperature of the individual months was 18 degreesC, as there were no months with an average between 17.9 and 18.8 degreesC. An average of 0.86 perinatal deaths with lethal malformations had spent their embryonic life in a cold month, whereas an average of 1.54 had spent their embryonic life in a hot month; in contrast, an average of 10.24 perinatal deaths with lethal malformations had spent their embryonic life in a cold month, and a smaller number (9.23) in a hot month. Conclusions. The perinatal deaths with lethal malformations therefore showed a significant tendency to have spent their embryonic lives during the hotter months in comparison with the other perinatal fetal deaths (p = 0.03). Further studies should be made with larger numbers of cases, maintaining careful attention to early perinatal data and local temperatures. (C) 2001 IMSS. Published by Elsevier Science Inc.