INTRODUCTION: Severe hypothyroidism in pregnancy is associated with maternal and foetal complications, and in less severe cases impaired neuropsychological foetal development is seen. The aim of the present study was to evaluate the efficiency of the clinical control suggested in the guidelines.

METHODS: This was a retrospective study of 93 consecutive pregnant women with hypothyroidism who were followed at Herlev Hospital in 2012. The thyroid function was evaluated upon confirmation of pregnancy and thereafter every fourth week. The aim of the treatment was a concentration of serum thyroid-stimulating hormone (S-TSH) less than 2.5 mU/l.

RESULTS: The frequency of an S-TSH of more than 4.1 mU/l was 39%. In 27% of all patients, a single measurement was made of a slight increase in S-TSH during the pregnancy, and only 12% had several increased S-TSH measurements exceeding 4.1 mU/l. Furthermore, 62% had a minimum of one S-TSH measurement above 2.5 mU/l. The pregnant women with increased S-TSH levels in the beginning of their pregnancy had a tendency to be overtreated later in their pregnancy.

CONCLUSION: Although a careful follow-up was performed, we found a high number of patients with a single occurrence of S-TSH outside of the recommended range during their first trimester. The high S-TSH values were registered during the first weeks of the pregnancy, but hereafter corrected, and the number of pregnancy complications recorded did not seem to differ from the number of complications in patients with a normal thyroid function. We recommend increased attention and monitoring of fertile women with hypothyroidism who are planning pregnancy.

FUNDING: not relevant.

TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02094079.