BACKGROUND: Maternal preconception blood pressure (BP) is associated with various adverse pregnancy outcomes, but its relationship with spontaneous abortion (SA) remains controversial. We aimed to evaluate the relationship between preconception BP and SA. METHODS: This population-based cohort study used data from participants in the National Free Preconception Examination Program between 2013 and 2019. Maternal preconception BP was categorized according to the 2017 ACC/AHA guidelines. The relationship between these BP categories and SA incidence was analyzed using multivariable logistic regression to generate adjusted odds ratios (aORs) with 95% confidence intervals (CIs). Additionally, restricted cubic splines were employed to assess the dose-response relationship between maternal BP and the risk of SA. RESULTS: The study included 7 067 998 women, of whom 208 508 (2.95%) experienced a SA. Maternal preconception elevated BP (aOR, 1.02; 95% CI: 1.00-1.05), stage 1 hypertension (aOR, 1.06; 95% CI: 1.04-1.08), and stage 2 hypertension (aOR, 1.25; 95% CI: 1.20-1.31) were all associated with an increased risk of SA, demonstrating a gradient relationship. Our results also show that there is a "J"-shaped dose-response relationship between maternal preconception BP and the risk of SA, with the lowest risk observed at a systolic BP of 110 mm Hg and a diastolic BP of 70 mm Hg. Sensitivity analyses excluding individuals with hypotension or self-reported hypertension yielded results consistent with the main analysis. CONCLUSIONS: Preconception elevated BP and stage 1 hypertension were associated with an increased risk of SA, although the strength of these associations was weaker than that observed for stage 2 hypertension. There was a "J"-dose-response relationship between maternal preconception BP and the risk of SA, with the lowest risk of SA at systolic BP of 110 mm Hg and diastolic BP of 70 mm Hg.
Yin et al. (Mon,) studied this question.