The influence of maternal BMI and gestational diabetes on pregnancy outcome

- In women who are overweight or obese on entering pregnancy the incidence of gestational diabetes increased with increasing maternal BMI.
- Women who were obese were significantly more likely to require a caesarean birth and deliver a large for gestational age infant when compared with women who were overweight, independent of GDM.
- Women with gestational diabetes were significantly less likely to give birth to a macrosomic infant, compared with women without gestational diabetes. Decreased risk of fetal macrosomia in this group of women is likely to reflect the effect of GDM treatment.
- Women with gestational diabetes are more likely to have their infant admitted to intensive care.

AimsTo evaluate the effect of maternal body mass index (BMI) on gestational diabetes (GDM) and the risk of adverse pregnancy outcomes in women who are overweight or obese.MethodsA prospective cohort study nested within the LIMIT randomised controlled trial. A total of 1030 women were recruited between 10 and 20 weeks' gestation, with a BMI ≥ 25 kg/m2, and were grouped into BMI subclasses utilising World Health Organisation criteria. Women underwent a fasting oral glucose tolerance test at 26-28 weeks' gestation, and a diagnosis of GDM was made if fasting blood glucose was ≥5.5 mmol/L or ≥7.8 mmol/L after 2 h. Maternal and neonatal health outcomes were evaluated.ResultsThe prevalence of GDM increased with increasing maternal BMI (6.74% overweight vs 13.42% obese subclass 1 vs 12.79% obese subclass 2 vs 20.00% obese subclass 3). Women who were diagnosed with GDM were significantly less likely to give birth to an infant with birth weight above 4 kg (RR 0.60; 95% CI 0.36 to 1.00; p = 0.05). The need for caesarean delivery (RR 1.27; 95% CI 1.07 to 1.50; p = 0.006) and incidence of birth weight >90% (RR 1.38; 95% CI 1.07 to 1.77; p = 0.01) was significantly increased in women who were obese, independent of GDM.ConclusionIncreasing maternal BMI is a significant risk factor for the development of GDM, and our findings demonstrate a considerably higher prevalence than has been previously described. Raised maternal BMI is a risk factor for high infant birth weight, which may be modified by lifestyle intervention.