Joint effect of maternal pre-pregnancy body mass index and folic acid supplements on gestational diabetes mellitus risk: a prospective cohort study

BACKGROUND: The joint effect of folic acid (FA) supplements and maternal pre-pregnancy body mass index (BMI) on gestational diabetes mellitus (GDM) has not been fully addressed. This study aimed to examine the joint effect of FA supplements and pre-pregnancy BMI on GDM. METHODS: Pregnant women at 4 to 14 weeks of gestation (n = 3186) were recruited during their first prenatal visit in Qingdao from May 1, 2019, to June 27, 2021. The main outcome was GDM at 24–28 weeks’ gestation. Screening was based on 75 g 2-hour oral glucose tolerance (OGTT), a fasting glucose ≥ 5.1 mmol/L, or a 1-hour result ≥ 10.0 mmol/L, or a 2-hour result ≥ 8.5 mmol/L. The interactive effect of FA supplements and pre-pregnancy BMI on GDM was examined using logistic regression analysis and ratio of odds ratios (ROR) was used to compare subgroup differences. RESULTS: Overall, 2,095 pregnant women were included in the analysis, and GDM incidence was 17.76%. Compared with women with pre-pregnancy BMI lower than 25.0 kg/m(2) and FA-Sufficient supplements ≥ 400 µg/day (FA-S) population, the adjusted odds ratios (aORs) of FA-S and FA-Deficiency supplements < 400 µg/d (FA-D) were 3.57 (95% confidence interval [CI]: 2.02–6.34) and 10.82 (95% CI: 1.69–69.45) for the obese women (BMI ≥ 30.0 kg/m(2)), and the aORs of FA-S and FA-D were 2.17 (95% CI: 1.60–2.95) and 3.27 (95% CI: 1.55–6.92) for overweight women (25.0 kg/m(2) ≤ BMI < 30.0 kg/m(2)). However, the risk of GDM did not differ significantly between the FA-D and the FA-S group in pre-pregnancy obese women (ROR = 2.70, 95%CI: 0.47–2.30), or overweight women (ROR = 0.66, 95%CI: 0.30–1.49). After further stratification of FA supplementation time, F-D and FA-S in obese women showed an interaction when FA supplement intake time < 3 months. However, there was no significant difference between subgroups (ROR = 1.63, 95% CI: 0.37–7.04). CONCLUSION: Maternal pre-pregnancy BMI was associated with the incidence of GDM, the dose of FA supplementation from pre-pregnancy to early pregnancy was not found to be related to the incidence of GDM. The dosage of FA supplement was not associated with GDM irrespective of maternal pre-pregnancy BMI.