Maternal exposure to ambient particulate matter on the growth of twin fetuses after in vitro fertilization

Background: While ambient air pollution has been associated with fetal growth in singletons, its correlation among twins is not well-established due to limited research in this area. Methods: The effects of exposure to PM2.5 particulate matter and its main components during pregnancy on birth weight and the incidence of large for gestational age (LGA) were investigated in 6177 twins born after in vitro fertilization at the Center for Reproductive Medicine of Shanghai Ninth People's Hospital (Shanghai, China) between 2007 and 2021. Other birth weight-related outcomes included macrosomia, low birth weight, very low birth weight, and small for gestational age (SGA). The associations of PM2.5 exposure with birth weight outcomes were analyzed using linear mixed-effect models and random-effect logistic regression models. Distributed lag models were incorporated to estimate the time-varying associations. Results: The findings revealed that an interquartile range (IQR) increase (18 mu g/m3) in PM2.5 exposure over the entire pregnancy was associated with a significant increase (57.06 g, 95 % confidence interval [CI]: 30.91, 83.22) in the total birth weight of twins. The effect was more pronounced in larger fetuses (34.93 g, 95 % CI: 21.13, 48.72) compared to smaller fetuses (21.77 g, 95 % CI: 6.94, 36.60) within twin pregnancies. Additionally, an IQR increase in PM2.5 exposure over the entire pregnancy was associated with a 34 % increase in the risk of LGA (95 % CI: 11 %, 63 %). Furthermore, specific chemical components of PM2.5, such as sulfate (SO42-), exhibited effect estimates comparable to the PM2.5 total mass. Conclusion: Overall, the findings indicate that exposures to PM2.5 and its specific components are associated with fetal overgrowth in twins.