Longitudinal trajectories of maternal TSH in healthy pregnant women in Catalonia

Objective: Longitudinal evaluation of thyroid function throughout pregnancy in the same subject could offer precise information about its dynamics as a physiological mechanism of adaption to the requirements. In this study, we evaluated longitudinal trajectories of maternal thyroid function during pregnancy by a latent class growth analysis and explored their association with maternal-fetal outcomes.Methods: A prospective observational study was carried out, including 414 healthy pregnant women, from the first trimester to delivery. Thyroid function and autoimmunity were measured in the three trimesters. Clinical data during pregnancy were obtained. Longitudinal mixed model techniques were performed to explore trajectories of gestational thyroid function.Results: Three different longitudinal trajectories were obtained from maternal thyrotropin (TSH) levels: low-increasing TSH (class 1) in 86% of cases, high-increasing TSH (class 2) in 9.7%, and decreasing TSH (class 3) in 4.3%. No statistical differences in free thyroxine levels were found among the three classes. Differences in maternal age (P = 0.027) and initial maternal weight (P = 0.043) were observed among the groups. In logistic regression analysis, maternal age correlated with longitudinal trajectories. The three longitudinal classes remain when women with thyroid autoimmunity (TAI) are excluded. Multinomial logistic regression showed maternal age correlated with longitudinal trajectories independently of TAI status.Conclusions: Three differentiated TSH trajectories were found in healthy pregnant women living in Catalonia, as previously described. No association with obstetric outcomes was observed in these different chronological thyroid pathways, but maternal age might condition the longitudinal mechanism of thyroid function regulation throughout pregnancy.