Abstract
Objectives: Exposure to air pollutants has been linked to preterm birth (PTB) after natural conception. However, few studies have explored the effects of air pollution on PTB in patients who underwent in vitro fertilization (IVF). We aimed to investigate the association between ambient air pollutants exposure and PTB risk in IVF patients.Methods: This retrospective cohort study included 2,195 infertile women who underwent IVF treatment from January 2017 and September 2020 in Hangzhou Women's Hospital. Totally 1,005 subjects who underwent a first fresh embryo(s) transfer cycle were analyzed in this study. Residential exposure to ambient six air pollutants (PM2.5, PM10, SO2, NO2, CO, O3) during various periods of the IVF timeline were estimated by satellite remote-sensing and ground measurement. Cox proportional hazards models for discrete time were used to explore the association between pollutants exposure and incident PTB, with adjustment for confounders. Stratified analyses were employed to explore the effect modifiers.Results: The clinical pregnancy and PTB rates were 61.2 and 9.3%, respectively. We found that PM2.5 exposure was significantly associated with an increased risk of PTB during 85 days before oocyte retrieval [period A, adjusted hazard ratio, HR=1.09, 95%CI: 1.02–1.21], gonadotropin start to oocyte retrieval [period B, 1.07 (1.01–1.19)], first trimester of pregnancy [period F, 1.06 (1.01–1.14)], and the entire IVF pregnancy [period I, 1.07 (1.01–1.14)], respectively. An interquartile range increment in PM10 during periods A and B was significantly associated with PTB at 1.15 (1.04–1.36), 1.12 (1.03–1.28), and 1.14 (1.01–1.32) for NO2 during period A. The stratified analysis showed that the associations were stronger for women aged <35 years and those who underwent two embryos transferred.Conclusions: Our study suggests ambient PM2.5, PM10, and NO2 exposure were significantly associated with elevated PTB risk in IVF patients, especially at early stages of IVF cycle and during pregnancy.
Highlights
IntroductionIt has been estimated that about 2.7 million (1.8–3.5 million) births globally were preterm in 2010 [2], while the rate of PTB in China was 7.1% in the same year, ranking second after India [3]
Preterm birth (PTB,
The multivariable adjusted Cox proportional hazards modeling showed that ambient PM2.5 exposure was significantly associated with an increased risk of PTB incidence among the participants during period A (85 days before oocyte retrieval), period B, period F and period I
Summary
It has been estimated that about 2.7 million (1.8–3.5 million) births globally were preterm in 2010 [2], while the rate of PTB in China was 7.1% in the same year, ranking second after India [3]. A growing number of studies have focused on the effects of air pollutants on adverse pregnancy outcomes, including PTB [8,9,10,11]. Several studies have demonstrated that air pollutants exposure may be associated with an increased risk of PTB [2, 8, 12, 13]. The results were still inconsistent, and the mechanisms whereby air pollutants could increase the PTB risk remain inconclusive. Most previous studies were conducted among pregnancies achieved through natural conception, and specific trimesters during pregnancy were examined, the effects of air pollution during the period before pregnancy remain unclear
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