Defining the normal – thyroid function and autoimmunity in pregnancy


Maternal thyroid hormones are necessary for fetal growth and development and transfer is secured by physiological alterations in maternal thyroid hormone economy which must be considered when evaluating maternal thyroid function. Although maternal thyroid dysfunction had been associated with adverse pregnancy outcomes, it was uncertain whether slight thyroid aberrations or autoimmunity were risk factors.

This thesis aimed to:
  •  Determine the effect of laboratory-specificity in pregnancy-specific thyroid hormone reference ranges
  •  Determine the prevalence of thyroid dysfunction and autoimmunity in healthy Danish pregnant women and associations with obstetric outcome
  •  Assess if thyroid autoimmunity was a risk factor

We found that not only gestational-age-specific, but also laboratory-specific, reference ranges were needed to evaluate maternal thyroid function. In 923 healthy pregnant women, 10% had thyroid dysfunction and 16.1% thyroid autoimmunity, but neither were associated with obstetric outcomes. By literature review, thyroid autoimmunity increased numerous obstetric and neonatal outcomes. However, randomized controlled trials showed no benefit of treating slight maternal thyroid aberrations.

We concluded that definitions of maternal thyroid function relied on laboratory-specific assays. Slight aberrations of thyroid function and thyroid autoimmunity were common and associated with adverse pregnancy outcomes, however, with insufficient evidence to support screening due to lack of evidence of treatment benefits.

Place of employment

PhD author

Date and place of defense

26th of March 2021, Auditorium 2, Rigshospitalet


Ulla Feldt-Rasmussen, professor, DMSci, MD
Copenhagen University Hospital (Rigshospitalet), Denmark

Claus Henrik Nielsen, professor, PhD, MD
Institute for Inflammation Research
Copenhagen University Hospital (Rigshospitalet), Denmark

Henriette Svarre Nielsen, professor, DMSci, MD
Recurrent Pregnancy Loss Unit
Copenhagen University Hospital (Rigshospitalet and Hvidovre Hospital), Denmark



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