Childhood secondhand smoke exposure and pregnancy loss in never smokers: the Guangzhou Biobank Cohort Study

Objective Studies of secondhand smoke (SHS) exposure especially childhood SHS exposure and pregnancy loss are limited. We used baseline data of the Guangzhou Biobank Cohort Study (GBCS) to examine the association of childhood SHS exposure with a history of pregnancy loss. Methods Never smoking women aged 50 years or above in GBCS from 2003 to 2008 were included. Propensity score matching (PSM) was used to control for confounding. Negative binomial regression and logistic regression were used to examine the association of childhood SHS, assessed by number of smokers in childhood household and frequency of exposure, with past pregnancy loss. Results Of 19 562 women, 56.7% (11 096) had SHS exposure during childhood. In negative binomial regression, after adjusting for age, education, past occupational dust exposure, past home fuel exposure, oral contraceptive, adulthood SHS exposure, age at first pregnancy and age at first menarche, compared to non-exposure, the incidence rate ratio of one more pregnancy loss was 1.20 (95% CI1.05 to 1.37) in those who lived with >= 2 smokers in the same household, and 1.14 (95% CI 1.04 to 1.25) in those exposed >= 5 times/week. After similar adjustment, logistic regression showed that the OR of pregnancy loss >= 2 times (versus 0 to 1 time) was 1.25 (95% CI 1.00 to 1.57) and 1.20 (95% CI 1.03 to 1.40) for high density (>= 2 smokers in the same household) and frequency (>= 5 times/week) of childhood exposure, respectively. Conclusions Childhood SHS exposure was associated with higher risks of pregnancy loss in middle-aged and older Chinese women.