Epidemiological studies suggest that both ambient ozone (O₃) and temperature were associated with increased risks of adverse birth outcomes. However, very few studies explored their interaction effects, especially for small for gestational age (SGA) and large for gestational age (LGA). To estimate the modification effects of ambient temperature on associations of ambient O₃ exposure before and during pregnancy with preterm birth (PTB), low birth weight (LBW), SGA and LGA based on multicity birth cohorts. A total of 56,905 singleton pregnant women from three birth cohorts conducted in Tianjin, Beijing and Maoming, China, were included in the study. Maximum daily 8-h average O₃ concentrations of each pregnant woman from the preconception period to delivery for every day were estimated by matching their home addresses with the Tracking Air Pollution in China (TAP) datasets. We first applied the Cox proportional-hazards regression model to evaluate the city-specific effects of O₃ exposure before and during pregnancy on adverse birth outcomes at different temperature levels with adjustment for potential confounders, and then a meta-analysis across three birth cohorts was conducted to calculate the pooled associations. In pooled analysis, significant modification effects of ambient temperature on associations of ambient O₃ with PTB, LBW and LGA were observed (P_interaction < 0.05). For a 10 μg/m³ increase in ambient O₃ exposure at high temperature level (> 75^th percentile), the risk of LBW increased by 28 % (HR: 1.28, 95% CI: 1.13-1.46) during the second trimester and the risk of LGA increased by 116% (HR: 2.16, 95%CI: 1.16-4.00) during the entire pregnancy, while the null or weaker association was observed at corresponding low (≤ 25^th percentile) and medium (> 25^th and ≤ 75^th percentile) temperature levels. This multicity study added new evidence that ambient high temperature may enhance the potential effects of ambient O₃ on adverse birth outcomes.

Objective: To investigate the prevalence of gestational diabetes mellitus (GDM) and its determinants among pregnant women in the Tongzhou district of Beijing, China. Methods: This study was performed on data collected in the routine work of the prenatal health care system from 27,119 pregnant women in the Tongzhou district of Beijing during 2013–2018. Univariate and multivariate logistic regression analyses were used to assess the factors associated with GDM. Results: The overall prevalence of GDM was 24.24%, and it showed an increasing trend over the 6 years. A univariate analysis showed that the prevalence of GDM increased with age (p < .001). In multivariate analysis, it was found that women with a non-local household registration, as well as those without a local household registration but whose husbands had one, had a lower risk for GDM than both spouses who had local registration. Women who were overweight/obese had a higher risk for GDM than women with a normal pre-pregnancy body mass index. Multipara women had a lower likelihood of developing GDM. Conclusions: We found a slightly higher prevalence of GDM in the Tongzhou district of Beijing than has been found in other studies, and the prevalence rose over the 6 years of the study. Advanced age, pre-pregnancy overweight or obesity, and local household registration were important risk factors for GDM. Multiparity may be a protective factor against developing GDM. Intensive health education on related determinants should be strengthened for the prevention and control of GDM, especially in high-risk women.

Objective: To examine changes in periconceptional folic acid supplementation behaviour among Chinese women of reproductive age after the implementation of a folic acid supplementation programme.Design: Two cross-sectional surveys were conducted.Setting: One survey was before (2002–2004) and the other was after (2011–2012) implementation of the programme, both were conducted in two areas of China with different prevalence of neural tube defects. Information on supplementation behaviours was collected in face-to-face interviews with women early in their pregnancy.Subjects: A total of 1257 and 1736 pregnant women participated before and after the programme, respectively.Results: The rate of periconceptional folic acid supplementation increased from 15 % to 85 % in the high-prevalence population and from 66 % to 92 % in the low-prevalence population. However, more than half of the women began taking the supplement after learning they were pregnant. The proportion of women who began taking folic acid before their last menstrual period decreased after the programme in rural areas with both a high and low prevalence of neural tube defects.Conclusions: Although periconceptional folic acid supplementation among Chinese women increased substantially after the programme, supplementation was often initiated too late to be effective in preventing neural tube defects. Educational and promotional campaigns should focus on how to increase the rate of folic acid supplementation before pregnancy.

To examine the role of total mercury (T-Hg) in placenta as a biomarker of prenatal mercury (Hg) exposure and determine the association between prenatal Hg exposure and risk for neural tube defects (NTDs) in offspring. Total Hg concentrations in placental tissue were detected in 408 NTD cases and 593 healthy controls enrolled in Shanxi province in northern China. Methylmercury (MeHg) and T-Hg were also detected in the umbilical cord of 147 NTD cases and 140 healthy controls. In addition, MeHg and T-Hg were detected in fetal kidney, liver, and brain tissues of 51 NTD cases. Spearman's rank correlation (rs) was used to evaluate the correlations between placental T-Hg and T-Hg in umbilical cord and fetal kidney, liver, and brain tissues. The Wilcoxon rank-sum test was used to compare T-Hg amounts between case and control groups. Logistic regression was used to examine the association between placental T-Hg and risk for NTDs. Placental T-Hg was significantly correlated with T-Hg in umbilical cord (rs = 0.479), kidney (rs = 0.718), liver (rs = 0.656), and brain (rs = 0.512) tissues (all p < 0.001). The median (25th percentile-75th percentile) concentration for placental T-Hg in the NTD case group was 8.91 (5.00-17.1) ng/g dry weight (d.w.), significantly higher than that in the healthy control group (4.99 [3.26-7.93] ng/g d.w., p < 0.001). After adjusting for potential confounders, higher levels of T-Hg in placenta were associated with increased risk for NTDs in offspring (OR = 1.76, 95% CI: 1.13-2.76), and a dose-response relationship was found (p < 0.001). The concentration of T-Hg in placenta is a good biomarker for estimating prenatal Hg exposure, which is associated with increased risk for NTDs.