Universal screening to detect hypothyroidism in pregnant women

Hypothyroidism may be detrimental when left undiagnosed, but universal testing of pregnant women is hitherto not implemented. We studied the implementation of a laboratory-guided universal screening model to detect hypothyroidism in pregnant women.

A prospective implementation study in the North Denmark Region during a 2-year period (2022-2024).

Serum residues of blood samples drawn from Danish pregnant women as part of prenatal screening for chromosomal anomalies in early pregnancy (median the 10th week) were used for measurement of thyroid-stimulating hormone (TSH), free thyroxine (fT4), thyroid peroxidase, and thyroglobulin antibodies (TPO-Ab and Tg-Ab) upon arrival in the laboratory. Results were clinically reported only if maternal TSH in the sample was above 6 mIU/L, and thyroid disease was not known. Overt/subclinical hypothyroidism was defined by fT4 below/within the method- and trimester-specific reference interval (10.2-15.2 pmol/L).

A total of 11 841 samples were screened from 10 403 pregnant women (median age of 30 years). Unknown maternal TSH above 6 mIU/L was identified in 41 women (0.39%) of whom 32 had overt and 9 had subclinical hypothyroidism. Thyroid-stimulating hormone ranged from 6.1 to 59.4 mIU/L and was above 10 mIU/L in 19 women. All screen-positive cases had detectable TPO-Ab and/or Tg-Ab, and the general practitioner was immediately informed for specialist referral and treatment.

This prospective study tested implementation of a universal screening model to detect maternal hypothyroidism in pregnancy. Clinical implementation was feasible, and 0.4% of Danish pregnant women were found to be screen positive, all with detectable thyroid autoantibodies, indicative of autoimmune hypothyroidism.