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Seventy-two thousand labor histories for a period of several years from 5 different obstetrical institutions of two geographical regions of the Soviet Union were sub­jected to retrospective analysis. Significant influence of preceding induced abortion on the sex ratio is shown. In all five samplings the total sex ratio among primi- and multiparae with no abortions in anamnesis was 106.8♂:100♀. When infants are born within 1 year, 1-2 years, 2 years and more after an artificial abortion the sex ratio is: 76:4♂:100♀ (p < 0.001); 91.2♂:100♀ (p < 0.001); 125.2♂:100♀ (p < 0.001) respectively. Spontaneous abortions do not affect the sex ratio. Preponder­ance of female infants after an artificial abortion may be explained by selective survival of female embryos connected with heterosis by X-chromosome.