Investigating the relationship between environmental air pollution exposure and abnormal gestational weight gain in twin pregnancies: a retrospective study.

Background: Gestational weight gain (GWG) is a critical indicator of the health and nutritional status of pregnant women and their fetuses. However, there is limited evidence on how air pollution affects abnormal GWG in twin pregnancies.

Methods: In this retrospective analysis of 3,598 twin pregnancies, participants were categorized into three groups based on GWG: optimal, inadequate, and excessive. We collected data on ambient air pollutants, including fine particulate matter (PM_2.5), inhalable particulate matter (PM₁₀), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), and ozone (O₃). Multivariable linear regression models examined the associations between air pollutant exposure in each trimester and GWG, analyzing pollutants both continuously and by quartiles. Logistic regression and trend analyses assessed the impact of these pollutants on the risks of inadequate and excessive GWG, adjusting for potential confounders. Restricted cubic spline (RCS) models visualized trimester-specific effects, and cumulative effects of extreme air pollution indices on GWG outcomes were evaluated using logistic regression.

Results: The results indicated that exposure to PM_2.5, PM₁₀, SO₂, NO₂, and CO during pregnancy was positively associated with GWG in twin pregnancies, while O₃ exposure was negatively associated. For inadequate GWG, PM_2.5, PM₁₀, and SO₂ were identified as risk factors in the first trimester, with aORs of 1.008 (95% CI: 1.001-1.015), 1.006 (95% CI: 1.001-1.010), and 1.033 (95% CI: 1.000-1.067), respectively. In the second and third trimesters, these pollutants exhibited protective effects, alongside NO₂ and CO. Conversely, O₃ in the third trimester was a risk factor for inadequate GWG, with an aOR of 1.054 (95% CI: 1.008-1.102). Regarding excessive GWG, in the first trimester, PM_2.5, PM₁₀, SO₂, NO₂, and CO acted as protective factors, with aORs of 0.987 (95% CI: 0.980-0.994), 0.992 (95% CI: 0.986-0.997), 0.956 (95% CI: 0.924-0.989), 0.972 (95% CI: 0.948-0.997), and 0.243 (95% CI: 0.075-0.787), respectively. However, their effects reversed in the second and third trimesters, becoming risk factors for excessive GWG, with more pronounced effects observed in the third trimester. O₃ remained a protective factor against excessive GWG in both the second and third trimesters, with aORs of 0.951 (95% CI: 0.905-0.999) and 0.876 (95% CI: 0.835-0.920), respectively. Finally, the effects of extreme air pollution exposure on GWG varied across different pregnancy stages. In the first trimester, extreme exposures to PM_2.5, PM₁₀, SO₂, and CO were associated with an increased risk of inadequate GWG, while NO₂ exposure appeared protective. In contrast, extreme air pollution exposure was protective against excessive GWG, with NO₂ exposure acting as a risk factor. By the second and third trimesters, extreme exposures to PM2.5, PM10, SO2, and CO became risk factors for excessive GWG.

Conclusion: The effects of ambient air pollutants on gestational weight gain in twin pregnancies vary by pregnancy stage, with extreme air pollution exposure exhibiting time-dependent characteristics. These findings highlight the complex, stage-specific relationship between air pollution and maternal weight gain during twin pregnancies.