Meeting Abstract

44.1  Sunday, Jan. 5 10:30  Gestational weight gain influences sex ratios at birth in humans NAVARA, KJ; Univ. of Georgia knavara@uga.edu

Previous studies in birds and non-human mammals suggest that females bias the sex ratios of offspring in response to resource limitations. In addition, a previous study in humans indicated that women with high levels of energy intake prior to conception produced more boys, and the numbers of boys produced by humans appears to drop in times of famine. It is unclear, however, whether these adjustments happen prior to or during gestation, as a primary or secondary adjustment of sex ratio. By analyzing sex ratios of over 85 million US births over 21 years, we tested whether the human sex ratio at birth was related to gestational weight gain and the development of gestational diabetes. We predicted that women who gain more weight and/or develop diabetes during gestation would produce more boys, and that, if the adjustment was happening during gestation, the sex ratios of fetal deaths would be more female-biased in women who gained more weight during gestation. Indeed, there was a near-perfect positive correlation between the amount of weight women gained during pregnancy and the percentage of boys produced (p < 0.0001), and women who developed gestational diabetes were more likely to produce boys (p < 0.0001). In addition, there was a negative correlation between the amount of weight women gained and the percentage of male fetal deaths, but only between 20-23 weeks of gestation (p = 0.02). These results suggest that from 20-23 weeks of gestation is a critical time during which weight gain can influence the survival of male or female offspring, and ultimately affect the sex ratio at birth.