Pregnancy-specific Reference Intervals for TSH and FT4: Novel Insights From Preconception-gestation Longitudinal Data
Authors' conclusion
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.
Study context
- Population
- Women in Generation R Next, a population-based prospective cohort from preconception through postpartum in Rotterdam
- Participants
- 2,084 / 2,084 / 1,058
- Exposure
- Pregnancy-specific vs nonpregnancy reference intervals for TSH and FT4 during pregnancy, compared with preconception
- Nonpregnancy reference intervalsn = 2,084
- Pregnancy-specific reference intervalsn = 2,084
- Preconceptionn = 1,058reference
- Outcome
- Prevalence of thyroid disease entities
Methodological detailspopulation-based, preconception through postpartum
- Population-based
- Preconception through postpartum
Main finding
As reported in the abstract
Prevalence of SCH
Observational data: associations, not effects.
Further findings
- Prevalence of subclinical hyperthyroidism — preconception
- 2.0%
- Prevalence of subclinical hyperthyroidism: Pregnancy, nonpregnancy RIs 11.1%
- Prevalence of subclinical hyperthyroidism: Pregnancy, pregnancy-specific RIs 1.5%
Subclinical hyperthyroidism cases reclassified to hyperthyroidism by additional free T3 (FT3) measurements
- Reclassified during preconception
- 5.6%
- Reclassified during pregnancy
- 14.3%
Original publication
Pregnancy-specific Reference Intervals for TSH and FT4: Novel Insights From Preconception-gestation Longitudinal Data. J Clin Endocrinol Metab. Published 28 February 2026. doi:10.
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