Elevated maternal serum bile acids level, hypertensive disorders of pregnancy and adverse fetal outcomes: a cohort study of 117,789 pregnant women in China

Background

Elevated maternal serum total bile acids (sTBA) level during pregnancy was associated with adverse fetal outcomes. Women with elevated sTBA could complicate with hepatic dysfunction or vascular disorders (hypertensive disorders of pregnancy, HDP), which aggravated adverse fetal outcomes. However, the relationships among sTBA level, hepatic dysfunction, HDP and adverse fetal outcomes were still illusive.

Objective

We aimed to explore whether hepatic dysfunction or vascular disorders (HDP) mediated the associations between elevated sTBA level and adverse fetal outcomes.

Methods

A large retrospective cohort study encompassing 117,789 Chinese pregnant women with singleton delivery between Jan 2014 and Dec 2022 was conducted. Causal mediation analysis was applied to assess the mediating role of hepatic dysfunction (alanine transaminase > 40 U/L) or HDP in explaining the relationship between high maternal sTBA level (≥10 μmol/L) and adverse fetal outcomes, including low birth weight (LBW), small for gestational age (SGA), and preterm birth (PTB).

Results

sTBA level were positively associated with LBW (adjusted odds ratio (aOR) = 1.40; [95 % confidence interval (CI): 1.24–1.59]), SGA (aOR=1.31; [95 % CI: 1.18–1.46]), and PTB (aOR=1.27; [95 % CI: 1.15–1.41]), respectively. The estimated proportions of the total associations mediated by HDP were 47 % [95 % CI: 31 %–63 %] for LBW, 24 % [95 % CI: 13 %–35 %] for SGA, and 34 % [95 % CI: 19 %–49 %] for PTB, excepting the direct effects of high sTBA level. The contribution of hepatic dysfunction as a mediator was weaker on the association between high sTBA level on fetal outcomes, as the proportions mediated and 95 % CI were 16 % [4 %–29 %], 4 % [-6%–14 %], 32 % [15 %–50 %] for LBW, SGA, and PTB, respectively. Moreover, the mediating effect of hepatic dysfunction was nearly eliminated after excluding cases of HDP in the sensitivity analysis.

Conclusions

The substantial mediating effects through HDP highlighted its significant role in adverse fetal outcomes associated with elevated sTBA level. The findings also provoked new insights into understanding the mechanism and developing clinical management strategies (i.e. vascular protection) for adverse fetal outcomes associated with elevated sTBA level.