Defining Gestational Thyroid Dysfunction Through Modified Nonpregnancy Reference Intervals: An Individual Participant Meta-analysis

J Clin Endocrinol Metab. 2024 Oct 15;109(11):e2151-e2158. doi: 10.1210/clinem/dgae528.

Abstract

Background: Establishing local trimester-specific reference intervals for gestational TSH and free T4 (FT4) is often not feasible, necessitating alternative strategies. We aimed to systematically quantify the diagnostic performance of standardized modifications of center-specific nonpregnancy reference intervals as compared to trimester-specific reference intervals.

Methods: We included prospective cohorts participating in the Consortium on Thyroid and Pregnancy. After relevant exclusions, reference intervals were calculated per cohort in thyroperoxidase antibody-negative women. Modifications to the nonpregnancy reference intervals included an absolute modification (per .1 mU/L TSH or 1 pmol/L free T4), relative modification (in steps of 5%) and fixed limits (upper TSH limit between 3.0 and 4.5 mU/L and lower FT4 limit 5-15 pmol/L). We compared (sub)clinical hypothyroidism prevalence, sensitivity, and positive predictive value (PPV) of these methodologies with population-based trimester-specific reference intervals.

Results: The final study population comprised 52 496 participants in 18 cohorts. Optimal modifications of standard reference intervals to diagnose gestational overt hypothyroidism were -5% for the upper limit of TSH and +5% for the lower limit of FT4 (sensitivity, .70, CI, 0.47-0.86; PPV, 0.64, CI, 0.54-0.74). For subclinical hypothyroidism, these were -20% for the upper limit of TSH and -15% for the lower limit of FT4 (sensitivity, 0.91; CI, 0.67-0.98; PPV, 0.71, CI, 0.58-0.80). Absolute and fixed modifications yielded similar results. CIs were wide, limiting generalizability.

Conclusion: We could not identify modifications of nonpregnancy TSH and FT4 reference intervals that would enable centers to adequately approximate trimester-specific reference intervals. Future efforts should be turned toward studying the meaningfulness of trimester-specific reference intervals and risk-based decision limits.

Keywords: pregnancy; reference values; thyroid function tests; thyroid gland; thyrotropin; thyroxine.

Publication types

  • Meta-Analysis

MeSH terms

  • Female
  • Humans
  • Hypothyroidism* / blood
  • Hypothyroidism* / diagnosis
  • Hypothyroidism* / epidemiology
  • Pregnancy
  • Pregnancy Complications* / blood
  • Pregnancy Complications* / diagnosis
  • Pregnancy Complications* / epidemiology
  • Pregnancy Trimesters / blood
  • Prospective Studies
  • Reference Values
  • Thyroid Function Tests* / standards
  • Thyrotropin* / blood
  • Thyroxine* / blood

Substances

  • Thyrotropin
  • Thyroxine