Male excess among anatomically normal fetuses in spontaneous abortions.

Estimates of the sex ratio in miscarriages, obtained mainly by cytogenetic or nuclear sexing methods, have yielded conflicting results. We report the results of a study of the anatomic sex ratio among embryos and fetuses derived from a consecutive series of 3,469 miscarriages. The overall sex ratio (M:F) was 1.25. The male excess was confined to normally formed specimens (1.30) and was present at all gestational ages up to 23 weeks and all sizes over 5 cm. Among malformed specimens the sex ratio was close to unity (0.92). Agreement between chromosomal and anatomic sexing was excellent, and the cytogenetic sex ratio among anatomically normal abortuses showed a similar excess of males. We hypothesize that an excess of anatomic males among fetal deaths suggests the presence of a discrete cause or causes that operate on normally formed embryos and fetuses, whereas loss of malformed embryos and fetuses may be due to other mechanisms that affect females as often as males.