The Dynamic Changes in Maternal Thyroid Parameters Across the Three Trimesters and Their Differential Effects on the Occurrence of Adverse Obstetric Outcomes

Objective: Thyroid parameters undergo significant dynamic changes during pregnancy. This study aimed to comprehensively analyze the impact of abnormal thyroid parameters in each trimester on the incidence of common adverse obstetric outcomes. Methods: Blood samples drawn for thyroid parameters in each trimester during the antenatal period were determined after the participants gave birth. Serum thyrotropin, free thyroxine, free triiodothyronine, anti-thyroid peroxidase antibody (TPOAb), and anti-thyroglobulin antibody (TgAb) levels were tested using electrochemiluminescence immunoassays. Results: Among all the participants, TAI and hypothyroxinemia in the first trimester (T1) were significantly related to an increased risk of gestational hypertension [OR=5.136, 95% CI 1.537–17.158 and OR=7.683, 95% CI: 1.890-31.229, respectively]. Additionally, subclinical hypothyroidism in T1 was independently associated with a higher risk of postpartum hemorrhage [OR = 38.063, 95% CI 2.091–692.834].Besides, subclinical thyrotoxicosis in T1 showed a significant correlation with a raised risk of small for gestational age [OR=14.650, 95% CI 1.221–175.760]. Among euthyroid women during the whole pregnancy, either TPOAb+ or TgAb+ in the third trimester was an independent risk factor of premature birth [OR=5.092, 95% CI 1.059-24.481] and low birth weight [OR=8.165, 95% CI 1.717-38.824], respectively. Conclusion: Our findings indicate the importance of screening thyroid parameters in early pregnancy and the need to dynamically monitor these parameters throughout the entire pregnancy.