Accepted for/Published in: JMIR Public Health and Surveillance
Date Submitted: Oct 23, 2023
Open Peer Review Period: Oct 23, 2023 - Nov 6, 2023
Date Accepted: Apr 29, 2024
(closed for review but you can still tweet)
Association of PM2.5 exposure and preterm birth in women with abnormal preconception thyrotropin levels: Findings from a large cohort study
ABSTRACT
Background:
Prior research has linked exposure to particulate matter with aerodynamic diameter ≤2.5 μm (PM2.5) with preterm birth (PTB). However, the modulating effect of preconception thyroid stimulating hormone (TSH) levels on the relationship between PM2.5 exposure and PTB has not been investigated.
Objective:
This study aimed to assess whether preconception TSH levels modulate the impact of PM2.5 exposure on PTB.
Methods:
This cohort study was conducted in Guangdong, China, as a part of the National Free Pre-pregnancy Checkups Project (NFPCP). PM2.5 exposure was estimated by the inverse distance weighting (IDW) method. To investigate the moderating effects of TSH levels on trimester-specific PM2.5 exposure and PTB, we used the Cox proportional hazards model. Additionally, to identify the susceptible exposure windows for weekly-specific PM2.5 exposure and PTB, we built distributed lag models incorporating Cox proportional hazards models.
Results:
A total of 633,516 women who delivered between January 1, 2014, to December 31, 2019, were included. 34,081 (5.4%) of them had abnormal preconception TSH levels. During the entire pregnancy, each 10 μg/m3 increase in PM2.5 was linked to elevated risks of PTB (HR=1.559, 95% CI,1.390-1.748), early preterm birth (EPTB, HR=1.559, 95% CI, 1.227-1.980), late preterm birth (LPTB, HR=1.571, 95% CI,1.379-1.791) among women with abnormal TSH levels. For women with normal preconception TSH levels, PM2.5 exposure during the entire pregnancy was positively associated with the risk of PTB (HR=1.345, 95% CI, 1.307-1.385), EPTB (HR=1.203, 95% CI, 1.126-1.285), LPTB (HR=1.386, 95% CI, 1.342-1432). The critical susceptible exposure windows were 3rd-13th and 28th-35th gestational weeks for women with abnormal preconception TSH levels, compared to 1st-13th and 21st-35th gestational weeks for those with normal preconception TSH levels.
Conclusions:
PM2.5 exposure was linked with a higher PTB risk, particularly in women with abnormal preconception TSH levels. PM2.5 exposure appears to have a greater effect on pregnant women who are in the early or late stages of pregnancy.
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