Spontaneous abortion, sex ratio and facial cleft malformations.

In family and reproductive data combined from five treatment centers, relating to 861 index cases with cleft lip (with or without cleft palate, CL+/-P), maternally recognized spontaneous abortions were found to be significantly less frequent in sibships including two or more cases of CL+/-P than in sibships including only one case. In data relating to 379 index cases with cleft palate (CP), maternally recognized spontaneous abortions were reduced to a degree short of formal significant in sibships including two or more cases of CP by comparison with sibships including only one case of CP. The sex ratio among the sibs of parents of CL+/-P index cases was elevated when the index case was the only affected child and reduced when the index case had one or more affected sibs. Considered in combination with the results of other investigations, these findings indicate the existence of inherited factors reducing abortion frequency in the sibships of CL+/-P index cases. These factors appear to be unrelated to those for liability to CL+/-P.