Seasonal variation in the incidence of cleft lip and palate based on the age of conception.

Background: The purpose of this study is to identify seasonal changes in the incidence of Cleft lip and Palate (CL/P) in our population.

Methods: All cases of isolated CL/P born in Puerto Rico from January 1998 through December 2002 were identified through the Puerto Rican birth defect registry. Conception dates were estimated based on the reported last menstrual period. All deliveries during this same period were recorded and their conception dates estimated in the same manner. The data was separated into 4 groups for each year studied corresponding approximately to the four seasons.

Results: 484 cases of CL/P were identified among 308,968 live births (incidence 1.57/1000 live births. The lowest incidence of CL/P was seen during fall and winter (1.24 and 1.38/1000 live births respectively) and the highest during spring and summer (1.77 and 1.97/1000 live births respectively) (p = 0.002). The seasons with the highest incidence correspond to the period when the least number of conceptions are occurring. Estimation of relative risks using winter as a reference point (relative risk of 1.0) showed a decrease in the risk of CL/P in fall to .89 (95th confidence interval 0.88 - 1.57), an increase in the risk to 1.28 (CI 1.16 - 2.03) during spring and 1.42 (CI 1.16 - 2.03) during summer.

Conclusions: The reported seasonal variation in incidence may be secondary to the action of yet to be identified teratogens acting on the population at large, or more likely, changes in activity and diet patterns of the population.