Association of longitudinal thyroid function parameters with preterm birth: a retrospective cohort study in Jinan, China

To investigate the associations of longitudinal pattern of thyroid function parameters, including thyroid stimulating hormone (TSH), free thyroxine (FT4) and thyroid peroxidase antibody (TPO-Ab), between first and third trimesters with premature birth (PTB). Participants were adult women had prenatal examination and delivery at the Jinan Maternal and Child Health care Hospital in 2022–2024. K-means clustering analysis was used for clustering longitudinal pattern of TSH, FT4 and TPO-Ab between first and third trimesters. Multivariate logistic regression model was utilized for associations of different variables with PTB risk. A subgroup analysis of age, thyroid function, pregnancy complications, prenatal examination in second trimester and cesarean delivery history was also conducted. Among 851 eligible participants, 123 had PTB. Without PTB history (OR = 0.21, 95%CI: 0.05–0.84), without cesarean delivery history (OR = 0.37, 95%CI: 0.17–0.80), without pregnancy complications (OR = 0.15, 95%CI: 0.09–0.26), having prenatal examination in second trimester (OR = 0.34, 95%CI: 0.19–0.61) and with persistent high level of FT4 (OR = 0.50, 95%CI: 0.29–0.83) were associated with decreased odds of PTB. Additionally, the association between FT4 and PTB was consistent across subgroups. A high level of FT4 in both first trimester and third trimester was significantly associated with decreased odds of PTB. However, the specific mechanisms that FT4 influencing potential PTB risk need further exploration.