The correlation between hemoglobin concentration and blood pressure during pregnancy in different trimesters

Background: Maternal hemoglobin (Hb) is related to nutritional status, and it widely fluctuates during pregnancy. However, the relationship between Hb and blood pressure (BP) during pregnancy is unclear. This study aimed to estimate the associations between maternal Hb in various trimesters and its changes with BP during pregnancy.

Methods: We conducted this study by using data from the Electronic Medical Record System (EMRS) database of Zhoushan Maternal and Child Care Hospital in Zhejiang Province, China. The pregnancy duration was divided into seven periods: before 14th, 14 to 17th, 18 to 22nd, 23 to 27th, 28 to 31st, 32 to 35th, and 36 to delivery; generalized estimating equations (GEE) and multiple linear regressions were used for exploring their associations.

Results: 8168 pregnant women in the first trimester were included in this study. Hb level decreased significantly from the first to late-second trimester and then increased but did not return to the level of the first trimester. After adjustment for the potential confounders, compared with women with Hb 110 ~ 119 g/L, those with Hb < 110 g/L had low systolic BP (SBP) and diastolic BP (DBP) in the second and third trimesters and those with Hb ≥ 120 g/L had high SBP and DBP in various trimesters. Furthermore, the dose-response effect was observed between them; except that those with Hb < 100 g/L had high SBP in T1 (β = 2.85, P = 0.012). Hb concentration changes during pregnancy were also positively associated with BP level. Furthermore, Hb had a higher effect on DBP than SBP. It is worth noting that the Hb concentration in > = 140 g/L groups had significantly higher SBP and DBP than the other groups. A significant nonlinear relationship was found between hemoglobin changes with both SBP and DBP in different gestational weeks (P non-linear < 0.05).

Conclusions: This study found that maternal Hb was positively associated with BP during pregnancy and maternal Hb > 120 g/L during pregnancy and increased maternal Hb from the first to third trimesters should especially be given more attention.