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.