The Correlation between the First Trimester Combined Test Results and Thyroid Stimulating Hormone Levels as Well as Its Effect on Pregnancy Outcomes

BACKGROUND: Determining the pregnancy outcomes with independent prognostic factors in the first trimester combined screening test and thyroid stimulating hormone (TSH) is a concern for practitioners. We aimed to evaluate the correlation between TSH and first trimester combined screening test levels and examine their effects on pregnancy outcomes in healthy pregnant women. METHODS: A total of 349 pregnant women in Izmir Ataturk Training and Research Hospital, Turkey with normal TSH values in the first trimester between 2015 and 2020 were enrolled. Patients were divided into two groups as 274 and 75 patients according to TSH values with 2,5 as cut-off value; their birth weights and weeks were compared. Patients were also divided into three groups according to gestational weeks; their TSH values and combined tests were compared. RESULTS: When grouped based on the TSH threshold value (2.5uIU/ml), no significant relationship was found between the combined test parameters and TSH levels. In the combined test, after grouping according to the week of gestation, a negative correlation was observed between free beta-human chorionic gonadotropin (β-hCG) and TSH measured at 11 weeks (P=0.040, r=−0.189). A significant negative correlation was found between free β-hCG and newborn birth weight (P=0.032, r=−0.199), TSH and delivery time (P=0.011, r=−0.235). CONCLUSION: Free β-hCG and TSH levels could guide practitioners for birth weight and early delivery, respectively. Postponing the combined test for patients with elevated serum TSH levels to between the 12th and 13th weeks of gestation may reduce false positives.