Perinatal significance of isolated maternal hypothyroxinemia identified in the first half of pregnancy

Brian M. Casey, Jodi S. Dashe, Catherine Y. Spong, Donald D. McIntire, Kenneth J. Leveno, Gary F. Cunningham

Research output: Contribution to journalArticlepeer-review

167 Scopus citations

Abstract

OBJECTIVE: To establish pregnancy-specific free thyroxine thresholds and to assess perinatal effects associated with isolated maternal hypothyroxinemia identified in the first half of pregnancy. METHODS: Stored serum samples from 17,298 women who previously underwent thyroid-stimulating hormone (TSH) screening in the first half of pregnancy were analyzed for free thyroxine (T4) concentrations and thyroid peroxidase antibodies. Women with a free T4 below 0.86 ng/dL but a normal-range TSH were identified to have isolated maternal hypothyroxinemia. Pregnancy outcomes in these women were compared to those with a normal TSH and free T4. Thyroid peroxidase antibody status and the relationship between TSH and free T4 were analyzed for these women and women with subclinical hypothyroidism. RESULTS: Isolated maternal hypothyroxinemia was identified in 233 women (1.3%). There were not any excessive adverse pregnancy outcomes in these women. Positive thyroid peroxidase antibody assays (greater than 50 international units/mL) were similar in normal women (4%) and those with isolated hypothyroxinemia (5%) but were greater in women with subclinical hypothyroidism (31%, P<.001). There was a negative correlation between TSH and free T4 in normal women (rs=-0.19, P<.001) and those with subclinical hypothyroidism (rs=-0.11, P=.007). The correlation in women with isolated hypothyroxinemia was not significant. CONCLUSION: Isolated maternal hypothyroxinemia has no adverse effects on perinatal outcome. Moreover, unlike subclinical hypothyroidism, there was a low prevalence of thyroid peroxidase antibodies and no correlation between TSH and free T4 levels in women with hypothyroxinemia, leading us to question its biological significance.

Original languageEnglish (US)
Pages (from-to)1129-1135
Number of pages7
JournalObstetrics and gynecology
Volume109
Issue number5
DOIs
StatePublished - May 1 2007

ASJC Scopus subject areas

  • Obstetrics and Gynecology

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