Influence of season on prevalence of cleft lip and palate.

According to the multifactorial threshold (MFT) model, cleft lip and palate (CLP) result from the influence of exogenous and endogenous genetic factors. Based on nearly 1000 cases of cleft lip with or without cleft palate treated in the clinic for maxillofacial surgery of the Martin-Luther University Halle-Wittenberg during the period 1946-1995, we investigated the influence of season on the occurrence of this malformation. Seasons of the year reflect various exogenous factors that may be accessible to prevention. The calculated date of conception served as comparison value between the study group and controls. The clefts of type III (CLP; P = 0.48), isolated CP (P = 0.933) or male patients with clefts of type I showed no significant deviation from the distribution in the control group over the year. We proved a significant maximum in spring, summer and autumn and a minimum in winter for the conception date of female patients with type I clefts (P = 0.033, relative risk = 2.6). Some of the seasonal factors implicated in the aetiology that play a role in the development of clefts could be: