Objective To determine if a low glycaemic index diet in pregnancy could reduce the incidence of macrosomia in an at risk group.
Design Randomised controlled trial.
Setting Maternity hospital in Dublin, Ireland.
Participants 800 women without diabetes, all in their second pregnancy between January 2007 to January 2011, having previously delivered an infant weighing greater than 4 kg.
Intervention Women were randomised to receive no dietary intervention or start on a low glycaemic index diet from early pregnancy.
Main outcomes The primary outcome measure was difference in birth weight. The secondary outcome measure was difference in gestational weight gain.
Results No significant difference was seen between the two groups in absolute birth weight, birthweight centile, or ponderal index. Significantly less gestational weight gain occurred in women in the intervention arm (12.2 v 13.7 kg; mean difference −1.3, 95% confidence interval −2.4 to −0.2; P=0.01). The rate of glucose intolerance was also lower in the intervention arm: 21% (67/320) compared with 28% (100/352) of controls had a fasting glucose of 5.1 mmol/L or greater or a 1 hour glucose challenge test result of greater than 7.8 mmol/L (P=0.02).
Conclusion A low glycaemic index diet in pregnancy did not reduce the incidence of large for gestational age infants in a group at risk of fetal macrosomia. It did, however, have a significant positive effect on gestational weight gain and maternal glucose intolerance.
Trial registration Current Controlled Trials ISRCTN54392969.