Maternal diet, particularly the quantity and quality of carbohydrate, influences maternal blood glucose concentrations. Eating carbohydrate foods with a high glycaemic index (GI) is postulated to result in feto-placental overgrowth and higher infant body fat. We hypothesized that low GI dietary advice at the first antenatal visit would improve fetal birth weight percentile and ponderal index (PI).

The PREGGIO study (ACTRN12610000174088) was a two-arm, parallel design randomized controlled trial comparing the effects of low GI (LGI) and healthy eating (HE) advice on pregnancy outcomes. Pregnant women attending for their initial obstetric or midwife appointment at Wollongong Hospital or Illawarra Private Hospital were invited to participate. Individual dietary counseling was given by a dietitian in one face-to-face visit.

A total of 691 women (age 29 ± 0.3 y, BMI 24.5 ± 0.3) were enrolled. There were no significant differences in the primary outcomes of fetal birth weight, birth centile (49.4 ± 1.7 vs 51.4 ± 1.7, p = 0.4) or PI (2.7 ± 0.0 vs 2.7 ± 0.0, p = 0.53) in the HE vs LGI groups respectively.  The prevalence of infants who were small or large for gestational age was similar in both groups (p = 0.81).  In multivariate regression analysis, dietary glycaemic load (GI x carbohydrate content) was the only significant dietary predictor (p = 0.046) of the primary outcomes after adjustment for type of delivery (spontaneous, Caesarian or instrumental) and gender, but explained less than 1% of the variation.

A low intensity dietary intervention in pregnancy with either a low GI or conventional healthy diet does not influence pregnancy outcomes in healthy women.