Maternal pre-pregnancy BMI, MTHFR polymorphisms, and the risk of adverse pregnancy outcomes in pregnant women from South China: a retrospective cohort study

BACKGROUND: Increasing evidence suggests an association between maternal pre-pregnancy body mass index (pre-BMI) and adverse pregnancy outcomes. However, the effects of methylenetetrahydrofolate reductase (MTHFR) polymorphisms on these relationships require further investigation. This study aimed to investigate whether the relationship between pre-BMI and the risk of adverse pregnancy outcomes was influenced by MTHFR gene polymorphisms. METHODS: A total of 5614 mother-fetus pairs were included in the study. The odds ratios (OR) of adverse pregnancy complications, including gestational diabetes mellitus (GDM), gestational hypertension (GHT), cesarean delivery (CS), and premature rupture of membranes (PROM), were estimated using adjusted logistic regression models and subgroup analysis. RESULTS: Pregnant women with higher pre-BMI values were positively related to the risk of GDM, GHT, and CS. In the subgroup analysis, underweight BMI was associated with a decreased risk of CS and GDM in pregnant women with the MTHFR A1298C AA or C677T CC genotype, while overweight/obese BMI was associated with an increased risk of GDM and CS in different MTHFR variants. Moreover, pregnant women with MTHFR A1298C AC + CC or C667T CC were found to have an increased risk of GHT in the MTHFR A1298C AA or C667T CT + TT genotype. A remarkable association was observed between the obesity group with MTHFR A1298C AC + CC (OR = 6.49, CI: 2.67–15.79) and the overweight group with the C667T CC genotype (OR = 4.72, CI: 2.13–10.45). CONCLUSIONS: MTHFR gene polymorphisms exert a modifying effect on the association between maternal pre-BMI and the risk of GHT, CS, and GDM. Pregnant women with a high pre-BMI with specific MTHFR genotypes should be considered for GHT development. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12884-023-05605-6.