Maternal and Neonatal Outcomes of Sub-clinical Hypothyroidism Treated With Levothyroxine in Pregnancy: A Retrospective Cohort Study

Introduction: The effect of sub-clinical hypothyroidism (SCH) in pregnancy has been controversial. Furthermore, the impact of levothyroxine replacement on improving outcomes in pregnant women with SCH is unknown. This study aimed to assess the maternal and neonatal outcomes of pregnant women with SCH who were treated with levothyroxine replacement. Methods: This retrospective chart review was conducted at a tertiary hospital in Iran between 2020 and 2022. All pregnant women who had given birth during the study period were recruited. Those who did not have thyroid function test results within 10-12 weeks, as well as those with SCH who did not have levothyroxine replacement, were excluded. The subjects were divided into two groups based on the 2017 American Thyroid Association (ATA) criteria: non-SCH (TSH values 0.27-2.5 mIU/L) and SCH (TSH values more than 4.0 mIU/L). The demographic, obstetric, maternal, and neonatal outcomes of both groups were compared. The Chi-square test was used to compare the categorical variables. Binary logistic regression was used to assess differences in categorical variables. Results: With a frequency of 10.5%, 935 women out of 8888 were diagnosed with SCH. In terms of age, educational level, living residency, medical insurance, access to prenatal care, and smoking status, there were no differences between the two groups. In terms of gestational age, parity, onset of labor, history of infertility, hypertension, cardiovascular disease, anemia, and overt diabetes, there were no differences between the two groups; however, gestational diabetes was more common in those with SCH. Compared with the non-SCH group, the prevalence and risks of gestational diabetes [19.8 vs. 14.2, odds ratio (OR) = 1.14, 95% confidence interval (CI) = 1.72-3.95] were significantly higher in the SCH group after controlling for confounding factors. There were no differences in neonatal outcomes between the two groups. Conclusions: Except for gestational diabetes, we found no significant adverse events in terms of maternal and neonatal outcomes among women with SCH who were treated with levothyroxine.