Hemoglobin concentrations in early pregnancy and their associations with adverse pregnancy outcomes in Western China: a population-based study.

Background: Despite the global standardization of hemoglobin (Hb) testing in early pregnancy, the impact of first trimester Hb concentrations on pregnancy outcomes remains inadequately understood. Also, the early pregnancy Hb concentrations have not been well documented in Western China. Therefore, this study aimed to assess the Hb concentrations during early pregnancy and their associations with adverse pregnancy outcomes in Western China.

Methods: This cross-sectional study used data from the Chengdu Maternal and Child Health Information System for pregnant women who delivered between January 1, 2019, and December 31, 2023. A total of 454,815 Chinese females aged 15 to 49 years with available first trimester Hb data, including those with singleton or multiple gestations, were included in the analysis. Multivariable logistic regression models were performed to estimate the adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for associations between Hb categories and adverse pregnancy outcomes.

Results: The average first trimester Hb concentration was 126.0 (SD 10.5) g/L, with 5.8% of pregnant women experiencing anemia during early pregnancy. Multivariable logistic regression analyses revealed significantly increased odds of developing gestational diabetes mellitus (GDM) and gestational hypertensive disorders (GHD) across increasing Hb concentration categories. Compared to Hb concentrations of 110-119 g/L, Hb ≥ 140 g/L was associated with elevated risk of GDM (aOR: 1.57, 95% CI: 1.52, 1.62) and GHD (aOR: 1.87, 95% CI: 1.79, 1.96). Moreover, both Hb ≤ 99 g/L (aOR: 1.15, 95% CI: 1.03, 1.29) and Hb ≥ 140 g/L (aOR: 1.20, 95% CI: 1.13, 1.26) were associated with higher odds of preterm birth compared to Hb concentrations of 110-119 g/L. In addition, the restricted cubic spline demonstrated a U-shaped relationship for cesarean delivery, low birthweight and small for gestational age (p < 0.001). However, no significant associations were found between first trimester Hb concentrations and the odds of stillbirth, Apgar score < 7 at 5 min, or Apgar score < 7 at 10 min (p > 0.05).

Conclusions: Our research findings suggest associations between first trimester Hb concentrations and various adverse pregnancy outcomes. We recommend interventions for early pregnancy anemia, particularly moderate to severe cases, and emphasize monitoring females with high Hb concentrations to reduce adverse outcomes.