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STUDY QUESTION Do prepregnancy peripheral leukocytes (PPLs) and their subsets influence the risk of spontaneous abortion (SAB)? SUMMARY ANSWER PPLs and their subsets are associated with the risk of SAB. WHAT IS KNOWN ALREADY Compelling studies have revealed the crucial role of maternal peripheral leukocytes in embryo implantation and pregnancy maintenance. Adaptive changes are made by PPLs and their subsets after conception. STUDY DESIGN, SIZE, DURATION This population-based retrospective cohort study was based on data from the National Free Pre-pregnancy Check-up Project (NFPCP) in mainland China. Couples preparing for pregnancy within the next six months were provided with free prepregnancy health examinations and counseling services for reproductive health. The current study was based on 1 310 494 female NFPCP participants aged 20–49 who became pregnant in 2016. After sequentially excluding 235 456 participants lost to follow-up, with multiple births, and who failed to complete blood tests, a total of 1 075 038 participants were included in the primary analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS PPLs and their subset counts and ratios were measured. The main outcome was SAB. A multivariable logistic regression model was used to estimate the odds ratio (OR) and 95% CI of SAB associated with PPLs and their subsets, and restricted cubic spline (RCS) was used to estimate the nonlinear exposure-response relationship. MAIN RESULTS AND ROLE OF CHANCE Of the included pregnant participants, a total of 35 529 SAB events (3.30%) were recorded. Compared to participants with reference values of PPLs, the ORs (95% CIs) of leukopenia and leukocytosis for SAB were 1.14 (1.09–1.20) and 0.74 (0.69–0.79), respectively. The RCS result revealed a monotonous decreasing trend (P nonlinear < 0.05). Similar relationships were observed for the neutrophil count and ratio, monocyte count, and middle-sized cell count and ratio. The lymphocyte ratio showed a positive and nonlinear relationship with the risk of SAB (P nonlinear < 0.05). Both eosinophils and basophils showed positive relationships with the risk of SAB (eosinophil P nonlinear > 0.05 and basophil P nonlinear < 0.05). LIMITATIONS, REASONS FOR CAUTION Chemical abortion events and the cause of SAB were not collected at follow-up. Whether women with abnormal PPLs had recovered during periconception was not determined. WIDER IMPLICATIONS OF THE FINDINGS PPLs and their subsets are associated with the risk of SAB. Leukopenia and neutropenia screening in women preparing for pregnancy and developing a feasible PPL stimulation approach should be emphasized to utilize the immune window of opportunity to prevent SAB. STUDY FUNDING/COMPETING INTEREST(S) This study was approved by the Institutional Research Review Board of the National Health and Family Planning Commission. This study was supported by the National Key Research and Development Program of China (grants 2021YFC2700705 [Y.Y.] and 2016YFC100307 [X.M.]) and the National Natural Science Foundation of China (grant no. 82003472 [L.W.]). The funding source was not involved in the study design, data collection, analysis and interpretation of the data, writing the report, or the decision to submit this article for publication. No competing interests. TRIAL REGISTRATION NUMBER N/A. [ABSTRACT FROM AUTHOR]

To comprehensively assess the association of husband smoking with wives' thyrotropin abnormality. This population-based retrospective cohort study included 2 406 090 Chinese reproductive-aged women who had participated twice in the National Free Pre-pregnancy Checkups Project between 2010 and 2020. Multivariate-adjusted odds ratios and 95% confidence intervals for subnormal and supranormal thyrotropin were estimated according to the husband's smoking status. Husband smoking at the first visit was associated with a 17% (15%–20%) and 26% (24%–28%) increased odds of subnormal thyrotropin and supranormal thyrotropin respectively compared to participants in neither-smoker group. In non-smoking participants with normal thyrotropin levels at the first visit, the corresponding increased risk of subnormal thyrotropin and supranormal thyrotropin at the second visit were 15% (12%–18%) and 19% (16%–21%) in contrast to participants without husband-smoking exposure. In non-smoking participants with abnormal thyrotropin levels at their first visit, husband smoking cessation was associated with 27% (17%–35%) and 36% (31%–40%) reduced odds of subnormal thyrotropin and supranormal thyrotropin at the second visit compared with the participants whose husband still smoking at the second visit. Husband smoking was associated with wives' subnormal thyrotropin and supranormal thyrotropin, and cessation of husband smoking could reduce the odds of thyrotropin abnormality. Couple-focused smoking intervention should be developed to reduce the burden of asymptomatic thyroid disease in females. • 1. Husband smoking was associated with both supranormal thyrotropin and subnormal thyrotropin. • 2. Husband smoking cessation decrease the odds of thyrotropin abnormality. • 3. We call couple-focused smoking cessation to reduce subclinical thyroid disease. [ABSTRACT FROM AUTHOR]