Maintaining a healthy lifestyle before pregnancy is associated with a substantially lower risk of developing gestational diabetes mellitus (GDM), a large prospective cohort study has found.

The Nurses Health Study II recruited 116,671 female nurses aged 24-44 in 1989. Data were collected at baseline and regularly thereafter on a variety of lifestyle factors.

For the purposes of the analysis a low-risk group was identified who had normal weight before pregnancy, took regular exercise, ate a healthy diet and who did not smoke.

Each lifestyle variable was carefully defined and scored. For example, a healthy diet was based on the US Department of Agriculture Healthy Eating Index and measured using food frequency questionnaires. Individual nurse’s scores were then ranked in quintiles. Data on time spent on physical activity, BMI and smoking were handled similarly.

After ten years’ follow-up, 20,136 singleton pregnancies had occurred in 14,437 women. There were 823 pregnancies affected by GDM.

Each lifestyle factor was found to be significantly and independently associated with the risk of developing GDM. The associations remained significant after adjustment for other known risk factors (increasing maternal age, high parity, family history of diabetes).

The incidence of GDM in the women with the healthiest lifestyles (non-smoking, most physically active i.e. ≥ 150 min/week of moderate to vigorous physical activity, healthiest eaters, BMI < 25 kg/m²) was 52% lower compared with all other pregnancies RR 0.48 (95% CI:0.38-0.61).

When compared with the women with the lowest lifestyle scores, who met none of the healthy lifestyle criteria (in other words the women who might be a target group for GPs to identify) the healthiest had an 83% lower risk of GDM, RR 0.17 (95% CI:0.12-0.25).

In 2001, a paper from the Nurses Health Study looking at incident diabetes in a cohort of nearly 85,000 female nurses over 16 years concluded that 91% of cases of diabetes could be attributed to habits and forms of behaviour that did not conform to the low-risk pattern.¹

Now the Nurses Health Study II has shown that similar lifestyle factors raise the risk of GDM.

GDM increases a woman’s risk of hypertension, pre-eclampsia, and developing type 2 diabetes after pregnancy. It causes fetal macrosomia, is associated with congenital abnormalities, and the children of GDM pregnancies are also at higher risk of developing diabetes.

This large well conducted study revealed significant associations between modifiable lifestyle factors and the occurrence of GDM. It seems highly likely that the link is significantly causal too.

The message for GPs is, as in many other conditions we see, to promote healthy lifestyle change effectively rather than just treat the consequences of its absence.

Dr Chris Barclay