The critical role of late-pregnancy glycemic control for perinatal outcomes: a prospective cohort study

The impact of late-pregnancy glycemic control on pregnancy outcomes, especially in women with normal oral glucose tolerance test (OGTT) in mid-pregnancy, remain unclear. This study aimed to explore the potential benefits of maintaining glycemic levels within the target range during late pregnancy for improving pregnancy outcomes. A prospective cohort study (2018–2022) categorized participants into four groups based on the results of OGTT in mid-pregnancy and late-pregnancy fasting blood glucose (FBG) level: (1) Persistent normoglycemic group (PNG): normal OGTT, FBG < 5.3 mmol/L; (2) Late-pregnancy isolated hyperglycemia group (LPIHG): normal OGTT, FBG ≥ 5.3 mmol/L; (3) Gestational diabetes mellitus (GDM) with target glycemic control group (GDM-TC): GDM diagnosis, FBG < 5.3 mmol/L; (4) GDM with suboptimal glycemic control group (GDM-SC): GDM diagnosis, FBG ≥ 5.3 mmol/L. Associations with adverse perinatal outcomes were assessed using multivariate logistic regressions and population attributable fractions (PAF). A total of 35,378 pregnant women were included. The average age and pre-pregnancy BMI of all participants were 32.04 ± 3.85 and 21.86 ± 3.34 kg/m2. Of the participants, 15.43% were diagnosed with GDM. Among those with GDM, 9.27% had elevated FBG (≥ 5.3 mmol/L) in third trimester, whereas 2.01% of participants with a normal OGTT showed high FBG levels in late pregnancy. Compared to PNG, the risk of premature birth was significantly higher in the LPIHG, GDM-TC, and GDM-SC groups, with odds ratios (ORs) of 3.228 (2.503–4.162), 1.267 (1.097–1.463), and 1.883 (1.354–2.619) respectively. More importantly, significantly higher risks of adverse pregnancy outcomes, including cesarean section, macrosomia, and large-for-gestational age (LGA), were found in LPIHG and GDM-SC groups, with ORs of 1.335 (1.130–1.578) and 1.529 (1.272–1.838) for cesarean section; 1.579 (1.200-2.076) and 1.921 (1.474–2.504) for macrosomia; 1.477 (1.165–1.873) and 2.121 (1.699–2.648) for LGA. Given optimal late-pregnancy glycemic control, the respective PAF estimates were 0.8% (cesarean section), 5.0% (premature birth), 1.2% (macrosomia), and 1.1% (LGA) for non-GDM women; and 4.8% (cesarean section), 5.3% (premature birth), 10.0% (macrosomia), 11.0% (LGA), and 9.6% (shoulder dystocia) for GDM women. This study suggests that the optimal late-pregnancy glycemic control is significantly associated with improved perinatal outcomes, even in women with normal OGTT in second trimester.