Effect of Maternal Subclinical Hypothyroidism on Congenital Hypothyroidism Screening Results: A Retrospective Cohort Study.

Objectives: This study aimed to evaluate the results of congenital hypothyroidism screening (CHS) in neonates born to women with subclinical hypothyroidism (SHT) during pregnancy and to identify maternal and neonatal characteristics associated with recall rate in CHS.

Study Design: This retrospective cohort study included nonrefugee pregnant women and newborn pairs who underwent thyroid function tests during prenatal follow-up between 2014 and 2017 and had neonatal CHS records. The women were evaluated overall and divided into euthyroidism (ET) and SHT groups according to their thyroid function tests. The groups were compared in terms of CHS results. Neonates with thyroid-stimulating hormone (TSH) levels <5.5 mIU/L were considered "normal," while those with values ≥5.5 mIU/L were "recall."

Results: The antenatal thyroid function data of a total of 22,383 pregnant women were analyzed. Of these, 71.6% were ET and 16.3% were diagnosed as SHT. Overall, the recall rate accounted for 5.34% of all CHS results and the recall rate was higher in the SHT group (7.10%) compared with the ET group (5.54%;  = 0.001). Being low birth weight (LBW) or large for gestation age (LGA), maternal TSH above the 97.5th percentile, and cesarean delivery increased the risk of recall in CHS ( ˂ 0.05).

Conclusion: The recall rate was higher among the neonates of mothers with SHT. Being LBW or LGA, maternal TSH above the 97.5th percentile and cesarean delivery increased the risk of recall in CHS.

Key Points: · SHT is the most common form of hypothyroidism in pregnancy.. · TSH elevation is higher among the neonates of mothers with SHT.. · Being LBW or LGA, and cesarean delivery also increase the risk of TSH elevation in infants..