Carrying a boy increases a pregnant woman’s risk of developing gestational diabetes: ICES study

The sex of a baby and gestational diabetes mellitus (GDM) can now provide insight into a woman’s risk of diabetes after delivery and in a subsequent pregnancy, according to a new study by researchers at the Institute for Clinical Evaluative Sciences (ICES).

GDM is a type of diabetes that occurs during pregnancy when changes in metabolism and the effects of a growing baby “unmask” underlying metabolic abnormalities in the women at risk. Even though GDM typically goes away after delivery, the woman’s underlying abnormalities explain why she remains at very high risk for developing Type 2 diabetes in the future.

The researchers found that women having a boy were three per cent more likely to develop GDM than women having a girl. This suggests that a male fetus leads to greater pregnancy-associated metabolic changes than a female fetus does. In contrast, women with GDM having a girl were at higher risk of developing Type 2 diabetes after pregnancy, because they must have had even worse underlying metabolic abnormalities to get GDM in the first place without the metabolic impact of a male fetus.

“Fetal sex is a previously unrecognized factor that is associated with maternal diabetic risk both after delivery and in a subsequent pregnancy,” said Dr. Baiju Shah, senior scientist at ICES and senior author of the study published today in the Journal of Clinical Endocrinology and Metabolism.

The researchers conducted a study with 642,987 Ontario women who were first-time mothers and gave birth to a baby between April 2000 and March 2010. The study found:

• Women who had a male baby (329,707) in their first pregnancy had a three per cent greater risk of GDM than women who had a female baby.
• Women who had GDM in their first pregnancy (23,302) had a 7 per cent higher risk of developing Type 2 diabetes before a second pregnancy, if their first baby was a girl.
• In women who had GDM in their first pregnancy, the sex of the baby in a second pregnancy was not associated with the recurrence of GDM whether the mother had delivered a boy in her first pregnancy or a girl.
• However, women who did not have GDM in their first pregnancy with a male baby had a slightly higher risk of developing GDM in their second pregnancy if they were carrying a boy.

The researchers add that while the differences are statistically significant, they are also very small.

“We have always thought a lot about how a pregnant mother’s health, behaviour and physiology can impact the health of her baby. But this study suggests that the baby can help us better understand the health of the mother, and can help us predict her risks for future diseases,” said Shah.

“Fetal sex and the natural history of maternal risk of diabetes during and after pregnancy,” was published today in the Journal of Clinical Endocrinology and Metabolism.

Author block: Ravi Retnakaran and Baiju R Shah.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.

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