A comparison of the maternal and perinatal outcomes of pregnant patients who are Euthyroid versus those with Subclinical Hypothyroidism treated with Levothyroxine using different TSH Cut-off levels

ABSTRACT

Introduction@#In 2017, the American Thyroid Association (ATA) revised their guidelines that when trimester and assay specific TSH reference intervals is unavailable, a TSH cut-off of 4.0 mIU/L replacing the previously recommended 2.5-3.0 mIU/L may be used to define maternal hypothyroidism. It states that levothyroxine treatment is considered if anti-TPO levels are elevated and TSH is between 2.5 mIU/L and the trimester-specific upper limit. These recommendations are a major departure from our current practice because the local TSH trimester-specific reference interval is not applicable due to a different assay used and the anti-TPO result is not readily available. In this population-based study, we aimed to determine and compare the maternal and perinatal outcomes of pregnant women who are euthyroid (TSH 0.3-2.4 mIU/L) versus those with subclinical hypothyroidism at different TSH cut-off levels (TSH 2.5-4.0 mIU/L, TSH 4.0-10.0 mIU/L) treated with levothyroxine.@*Methods@#This is a single-center, prospective cohort study conducted at Chong Hua Hospital, Cebu City from September 2017 to September 2018 where a total of 505 pregnant women qualified. The cohort was divided into three groups the euthyroid group of 404 women with TSH 0.3-2.4 mIU/L as control subjects; 101 women with subclinical hypothyroidism treated with levothyroxine further subdivided into TSH level 2.5-4.0 mIU/L (81 women) and TSH level >4.0-10.0 mIU/L (20 women). These patients were followed through to delivery to document and compare the maternal and perinatal outcomes versus euthyroid patients.@*Results@#There was no statistically significant difference among the group of patients with subclinical hypothyroidism treated with levothyroxine versus euthyroid patients in documented complications of pregnancy, such as GDM, gestational HPN, pre-eclampsia, PROM, low APGAR score and fetal distress. However, in patients with baseline TSH 2.5-4.0 mIU/L there was preterm delivery in six (7.41%) patients, post-term delivery in two (2.5%) patients, with seven (8.6%) small for gestational age (SGA) infants and two (2.5%) large for gestational age (LGA) infants. In patients with baseline TSH > 4.0-10.0 mIU/L, preterm delivery occurred in two (10%) patients. In secondary analysis adjusted for age and parity at enrolment, pregnant women treated with levothyroxine at baseline TSH 2.5-4.0 mIU/L and TSH > 4.0-10.0 mIU/L versus the untreated women with TSH < 2.5 mIU/L showed no difference in the maternal and perinatal outcomes of pregnancy measured. @*Conclusion@#This study has shown a 12.5% prevalence of subclinical hypothyroidism in our setting. There was no difference in the maternal and perinatal outcomes of pregnant patients who are euthyroid versus those with subclinical hypothyroidism treated with levothyroxine at a TSH threshold of 2.5-4.0 mIU/L and >4.0-10.0 mIU/L. These findings support the view that levothyroxine treatment in pregnant women with subclinical hypothyroidism at a TSH cut-off of 2.5 mIU/L shows no harmful effects.