Seasonality, incidence, and sex distribution of cleft lip and palate births in Trent Region, 1973-1982.

The birth dates of 930 children born in the Trent Region 1973-1982 with a diagnosis corresponding to cleft palate, or cleft lip with or without cleft palate, was obtained from Hospital Activity Analysis. These data were analyzed to look at the incidence of clefting, sex distribution, and seasonal variation. The results obtained show a significant peak incidence of cleft palate births in August and September, with a low incidence in March to May. Cleft lip, with or without cleft palate, shows a different seasonal trend, with peak occurrence in December and January and a low frequency in May and June. These seasonal trends may act as a pointer to the environmental factors active in the multifactorial etiology of cleft lip and cleft palate.