Intervalos de referencia específicos del embarazo para TSH y FT4: nuevas perspectivas a partir de datos...

Pregnancy-specific changes in thyroid physiology have prompted the use of pregnancy-specific reference intervals to diagnose thyroid disease. However, such reference intervals are not widely available, and there is no evidence of their superiority over non-pregnancy reference intervals. Preconception data are understudied benchmarks to compare pregnancy-specific and non-pregnancy-specific intervals. Moreover, the added value of FT3 measurements, for example in cases of (subclinical) hyperthyroidism, remains to be quantified.

This study was embedded within Generation R Next, a population-based prospective cohort from preconception through postpartum in Rotterdam. Prevalence of thyroid disease entities was assessed using both pregnancy-specific and non-pregnancy reference intervals during pregnancy, and using non-pregnancy reference intervals in the preconception period. FT3 concentrations of both euthyroid participants and those with thyroid disease entities were compared in the preconception period and during pregnancy.

The study population included 1,058 women during preconception and 2,084 women during pregnancy. The prevalence of subclinical hypothyroidism during pregnancy was 1.5% with use of non-pregnancy reference intervals and 3.6% with pregnancy-specific reference intervals, versus 2.2% during preconception. The prevalence of subclinical hyperthyroidism during pregnancy was 11.1% with use of non-pregnancy reference intervals and 1.5% with pregnancy-specific reference intervals, versus 2.0% during preconception. Additional FT3 measurements would reclassify 5.6% of subclinical hyperthyroidism cases to hyperthyroidism during preconception and 14.3% during pregnancy.

This is the first study to assess the prevalence of (sub)clinical thyroid disease during pregnancy comparing non-pregnancy and pregnancy-specific reference intervals, while also comparing these prevalences to preconception data from the same source population. We show that pregnancy-specific reference intervals likely result in overdiagnosis of subclinical hypothyroidism and that FT3 has limited value in diagnosing (sub)clinical thyroid disease during pregnancy.