Effects of exposure to phthalate during early pregnancy on gestational diabetes mellitus: a nested case–control study with propensity score matching

Owing to the complexity of phthalates (PAEs) components and the diversity of their sources, the health hazards of their metabolites to pregnant women remain unclear. This study aimed to explore the relationship between exposure to PAEs during early pregnancy and gestational diabetes mellitus (GDM) in rural pregnant women. We assessed pregnant women with (n = 338) or without (n = 3082) GDM from the ongoing Zunyi Birth Cohort. Participants’ urine samples were collected to measure the levels of 10 metabolites of PAEs. GDM was diagnosed using the 75-g oral glucose tolerance test at 24–28 weeks of gestation. We adopted propensity score matching based on GDM-related factors and pregnant women’s backgrounds to establish two groups of 338 patients: those with or without GDM. In the cohort, we included 5734 pregnant women; 519 of them developed GDM, yielding a GDM incidence rate of 9.05%. Urinary concentrations of monooctyl phthalate (MOP), mono-benzyl phthalate (MBzP), mono(2-ethyl-5-oxyhexyl) phthalate (MEOHP), and mono(2-ethyl-5-carboxypentyl) phthalate (MECPP) during early pregnancy were significantly associated with GDM (P < 0.05). Logistic regression models revealed that MEOHP in the urine was positively associated with GDM (odds ratio [OR] = 1.55; 95% confidence interval [CI]: 1.00–2.39). Furthermore, restricted cubic spline models revealed that urine MEOHP concentrations greater than 15.6 μg/L were positively associated with GDM, and approximately 23.5% pregnant women had urine MEOHP concentrations greater than 15.6 μg/L. Thus, approximately 23.5% of pregnant women were at the risk of developing GDM due to MEOHP, which suggested that pregnant women should reduce the use of packaged food and cosmetics to reduce the risk of GDM. However, further molecular biology experiments are required to confirm these findings and to elucidate the underlying mechanisms.