Ecocytogenetic Observation on the Sex Ratio in the First Trimester

Abstract

The sex ratio at an early embryonic stage was investigated in 1100 cases of induced abortions terminated within 12 weeks of gestation. By means of the cytogenetic analysis of the chorionic villi, the sex ratio was determined as 107.5 (570 males/530 females), which did not seem to be different greatly from the ratio at birth. Since a slight excess of male conceptuses was already evident at this stage, it was suggested that main contributing factors affecting the male dominant sex ratio might be present at an earlier embryonic stage, namely the preimplantation, rather than later stages towards birth.