Sex ratio: a statistical association with the type and time of insemination in the menstrual cycle
Guerrero, R.
International Journal of Fertility 15(4): 221-225
1970
ISSN/ISBN: 0020-725X PMID: 5487546 Document Number: 470963
To determine the influence of time any frequency of mating (or insemination in the case of artificial insemination) on the human sex ratio at birth, 1823 records of single pregnancies were analyzed jointly by the Universidad del Valle Medical School (Cali, Columbia) and the Harvard School of Public Health (Boston). While analysis of all cases showed no significant differences in the probability of conceiving a male child relative to time of insemination, separate analysis of natural insemination (NI) and artificial insemination (AI) data revealed two clearly opposite and significant trends (P.01). In AI, there was an excess of girls when insemination had taken place three or more days before the shift in Basal Body Temperature (BBT) or one or more days after. In NI, there was an excess of boys for inseminations taking place four or more days before the BBT shift or one or more days after, and the probability of boys decreased in the days surrounding the shift. The trend was found to sharpen in individual analyses of cases involving only single inseminations and clear shifts in the BBT, as well as in AI when only donor inseminations were considered. The NI trend was also present when rhythm and infertility cases were analyzed individually, while a significant difference in distribution of days of insemination was also observed. Rhythm cases displayed a greater spread of insemination days than infertility cases which was thought to be the result of the fact that rhythm cases generally attempt to avoid thermal shift days while infertility patients deliberately aim for them.