What Should be the Thyroid Stimulating Hormone Cut-off Level in the First-Trimester Screening? A prospective Cohort Study and Mini Review of The Guidelines

Abstract

Aim: Thyroid Stimulating Hormone (TSH) and Human Chorionic Gonadotropin (hCG) are glycoproteins that the alpha subunit common. As a consequence of this, hCG has intrinsic thyrotropic activity. Because of high levels of hCG, maternal serum thyrotropin level is seen to decrease in 80% of pregnancies. Novel investigation and several commission opinions recommend that the TSH cut-off value should be 2.5 mU/L in the first-trimester thyroid function screening.. We aimed to evaluate the contributions of the maternal serum TSH cut-off value of 2.5 mU/L to the development of maternal and fetal complications. Materials and Methods: We constructed the study with pregnancies in their first 12 weeks and planned to do only observation prospectively. We excluded pregnant women with systemic disease and any history of thyroid surgery or thyroid pathology. According to the TSH level, a case group(TSH level >2.5 mU/L) and a control group (TSH level<2.5 mU/L) were created through the pregnants with normal Thyroxine (T4) levels. The cohort group were divided into four subgroups according to whether they were anti-thyroid peroxidase (anti-TPO) positive or not. We observed the fetomaternal outcomes like pregnancy loss, hyperemesis gravidarum, hypertensive disorders, gestational diabetes, prelabour rupture of membranes, placental abruption, with routine prenatal visits until delivery; also delivery style, birth weight, shoulder dystocia, newborn intensive care needs, and postpartum hemorrhage were recorded. Results: The incidence of miscarriage in the subgroup with TSH >2.5 mU/L and anti-TPO (+) was significantly higher than in those with TSH <2.5 mU/L and anti-TPO (+) (p<0.05). All groups had no significant difference in other maternal or fetal/neonatal complications. Conclusion: If only the population-based nomograms are created, we may advise maternal serum TSH level as <2.5 mU/L for first-trimester screening. Single or multiple pregnancy status, gestational age, and the presence of thyroid peroxidase antibodies should also be taken into account when creating these nomograms.