Objective  To evaluate effects of maternal overweight/obesity and white blood cell count (WBCC) during first trimester on gestational blood glucose level.

  Methods  We extracted records of 30 792 women with singleton pregnancy attending their first antenatal care visit before 13 gestational weeks in 7 urban districts of Tianjin city between 2009 through 2010 from Tianjin Maternal and Child Health Information System. The collected information of the women included demographics, general status of the pregnancy, WBCC and body mass index (BMI) during the first trimester, and 50 g oral glucose challenge test (GCT). Multivariable logistic regression was performed to assess independent and joint effects of WBCC and overweight/obesity in first trimester on blood glucose level in during pregnancy.

  Results  For all the pregnant women the median of WBCC was 8.2 × 10⁹/L, with the quartile cutoff values of 6.9 × 10⁹/L – 9.7 × 10⁹/L, and 19.9% of the women had the WBCC of greater than 10 × 10⁹/L and 18.8% of the women had the GCT of ≥ 7.8 mmol/L. The results of multivariate logistic regression analysis revealed that the women with the WBCC of > 10 × 10⁹/L during the first trimester had an increased risk of elevated blood glucose level in the second trimester (odds ratio OR = 1.271, 95% confidence interval CI: 1.186 – 1.362) compared to those with the WBCC of ≤ 10 × 10⁹/L. The pregnant women with overweight (BMI: 24.0 – 27.9 kg/m²) and obesity (BMI ≥ 28.0 kg/m²) during the first trimester had an increased risk of elevated blood glucose level (for overweight: OR = 1.553, 95% CI: 1.445 – 1.669; for obesity: OR = 1.801, 95% CI: 1.608 – 2.016) in comparison with those with normal weight (BMI: 18.5 – 23.9 kg/m²). Compared to those with low WBCC (≤ 10 × 10⁹/L) and low BMI (< 24 kg/m²), the pregnant women with high WBCC (> 10 × 10⁹/L) but low BMI had an OR of 1.257 (95% CI: 1.151 – 1.371) for elevated blood glucose but the OR increased to 2.162 (95% CI: 1.946 – 2.402) for the women with both high WBCC and high BMI (≥ 24 kg/m²); the results suggested a significant additive interaction of the two variables on blood glucose level which was verified by the statistical significance of the three indicators (relative excess risk, attributable proportion, and synergy index of the interaction).

  Conclusion  High WBCC during the first trimester is an independent risk factor for elevated blood glucose during pregnancy and overweight and obesity could promote the elevation of blood glucose interactively with WBCC in an additive manner among pregnant women.