Endocrine Abstracts

Background/aims: Maternal subclinical hypothyroidism has been reported to be associated with risks of adverse pregnancy outcomes such as fetal loss and possible fetal neurodevelopmental deficit. However, current guidelines seem to overestimate subclinical hypothyroidism in pregnant women in some regions. Therefore, we aim to evaluate trimester-specific reference range of serum TSH for pregnant women in Korea and whether maternal subclinical hypothyroidism affects perinatal outcomes.

Methods: This is a prospective, observational study conducted in Samsung Medical Center between April 2012 and September 2013. Total 348 pregnant women who visited obstetrics for antenatal check-up were enrolled. Women with previous thyroid diseases or medications, positive for autoantibodies, multifetal gestation were excluded.

Results: Mean values of serum TSH in the first, second and third trimester were 1.22, 1.65 and 1.69 mIU/l respectively. Reference intervals (2.5%, 97.5%) of serum TSH in each trimesters as follows; 0.04–4.07, 0.09–4.85 and 0.32–6.07 mIU/l, respectively. According to current guidelines, 25.5% of subjects in the first trimester were diagnosed as subclinical hypothyroidism, 12.9% in the second trimester and 12.3% in the third trimester, respectively. Additionally, perinatal outcomes of these women were not different with that of subjects with normal TSH value.

Conclusions: Upper limit of reference value of serum TSH is much higher in Korean pregnant women than that of current guidelines and needs to be modified. Perinatal outcomes are favorable in pregnant women with subclinical hypothyroidism and further studies are needed to clarify long-term neurodevelopmental outcomes of offspring.