Sex ratio variations among the offspring of women with diabetes in pregnancy.

AIMS: It has long been hypothesized that natural selection would favour a reproductive strategy biased towards females under adverse circumstances in order to maximize the number of surviving grandchildren. An excess of daughters in women with Type 1 diabetes and a greater likelihood of gestational diabetes in women carrying male fetuses have also been reported. This study aims to compare the sex ratio across categories of maternal glycaemia.
METHODS: Among 288,009 mother-infant pairs delivering at Kaiser Permanente Northern California in 1996-2008, sex ratios were calculated for the following categories: pregravid diabetes, gestational diabetes, mild pregnancy hyperglycaemia (defined as an abnormal screening but normal diagnostic test for gestational diabetes) and normoglycaemia. Odds ratios for delivering a male were estimated with logistic regression; normoglycaemic pregnancies comprised the reference.
RESULTS: Women with pregravid diabetes delivered the fewest males (ratio male/female = 1.01), followed by women with normoglycaemic pregnancies and those with an abnormal screening only (both sex ratios = 1.05); women with gestational diabetes delivered the most males (sex ratio = 1.07). Odds ratio estimates suggested the same pattern, but none attained statistical significance.
CONCLUSIONS: The crude sex ratios in this cohort suggest a possible gradient by category of maternal glycaemia. Women with gestational diabetes, a condition characterized by excessive fuel substrates, appear to deliver more males. Women with pregravid diabetes delivered the fewest males, possibly reflecting the unfavourable state of chronic disease.