Aims/hypothesis: It has recently emerged that carrying a male fetus may be associated with poorer maternal beta cell function and an increased risk of gestational diabetes mellitus (GDM). Recognising that the overall impact of fetal sex on maternal glucose metabolism is likely to be subtle, we sought to perform a systematic review and meta-analysis of observational studies to obtain a robust estimate of the incremental maternal risk of GDM associated with the sex of the baby.
Methods: We searched PubMed and EMBASE to identify observational studies published between 1 January 1950 and 4 April 2015 that reported data on fetal sex and the prevalence of GDM. Two independent reviewers extracted the data and pooled estimates of the RR were calculated by a random-effects model. We considered male fetus as the exposure and prevalence of GDM as the outcome of interest.
Results: We identified 320 studies through electronic searches and nine studies through manual searches. Twenty studies met the inclusion criteria, yielding data on 2,402,643 women. Pooled analysis of these studies demonstrated an increased risk of GDM in women carrying a male fetus compared with women carrying a female fetus (RR 1.04; 95% CI 1.02, 1.06). This result was confirmed in a sensitivity analysis including only studies that applied a stringent definition of GDM (RR 1.03; 95% CI 1.01, 1.06) (I(2) = 0%, p = 0.66).
Conclusions/interpretation: Pregnant women carrying a boy have a 4% higher relative risk of GDM than those carrying a girl. The fetus thus may have previously unsuspected effects on maternal glucose metabolism in pregnancy.
Keywords: Beta cell function; Fetal sex; Gestational diabetes; Male fetus; Meta-analysis; Systematic review.