Body mass index and hemoglobin concentration have an additive effect on blood pressure among pregnant women in Guangxi, China

Background: Body mass index (BMI) and hemoglobin (Hb) are positively associated with hypertensive disorders in pregnancy. The aim of this study was to estimate a potential interaction between high BMI and high Hb concentrations on systolic blood pressure (SBP) and diastolic blood pressure (DBP) among pregnant women. Methods: We recruited 4497 single-birth women aged 18–43 years who received routine antenatal care from three hospitals of Guigang, Guangxi, China. Relevant data were derived from medical records of each woman. Multivariable linear regression was used to evaluate the association of high BMI and high Hb concentrations with SBP and DBP by trimesters of pregnancy. Results: In multivariable analyses, BMI was positively associated with SBP throughout all trimesters, and higher Hb concentrations was associated with increased SBP only in the first trimester (all P for trend <0.05). BMI and Hb concentrations were positively associated with DBP in the first and third trimesters (all P for trend <0.05). The average differences in SBP and DBP comparing women with high BMI and high Hb concentrations to those with non-high BMI and non-high Hb were 1.6 mmHg (95% CI: -0.3 to 3.5 mmHg) and 2.4 mmHg (95% CI: -0.1 to 4.8 mmHg) in the first trimester, 1.4 mmHg (95% CI: -1.4 to 4.2 mmHg) and 1.0 mmHg (95% CI: -1.7 to 3.7 mmHg) in the second trimester, and 2.9 mmHg (95% CI: 0.3 to 5.4 mmHg) and 3.5 mmHg (95% CI: 1.0 to 5.9 mmHg) in the third trimester, respectively. Conclusion: Our findings suggest that high BMI and high Hb concentrations may have interactions of additive effects on increased SBP and DBP in late stages of pregnancy.