<p>Recent studies on maternal exposure to air pollution and preterm birth (PTB) have yielded inconsistent results, with varying critical windows of exposure. This study aims to explore the association between air pollution and the risk of preterm birth in different subtypes of twin pregnancies, while identifying the sensitive time windows. In this retrospective study, we analyzed 3623 twin-pregnant women, categorized by timing and clinical condition of preterm birth. We used restricted cubic splines (RCS) and multivariable logistic regression to examine the effects of air pollution on different preterm birth subtypes. The results indicate that air pollution exposure during twin pregnancy significantly increased the risk of late-PTB and sPTB. In the third trimester, exposure to PM_2.5, PM₁₀, SO₂, NO₂, and CO increased the risk of late-PTB. Six pollutants were associated with higher sPTB risk throughout pregnancy, particularly in late pregnancy, with more pronounced increase. These results suggest that late pregnancy may be a critical window for the impacts of air pollution on twin pregnancies. These findings provide important scientific evidence to manage air pollution-related PTB risks in twin pregnancy.</p>