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756726 
Journal Article 
Perinatal significance of isolated maternal hypothyroxinemia identified in the first half of pregnancy 
Casey, BM; Dashe, JS; Spong, CY; Mcintire, DD; Leveno, KJ; Cunningham, GF 
2007 
1 
Obstetrics and Gynecology
ISSN: 0029-7844
EISSN: 1873-233X 
LIPPINCOTT WILLIAMS & WILKINS 
PHILADELPHIA 
109 
5 
1129-1135 
English 
17470594 
WOS:000246771600018 
To establish pregnancy-specific free thyroxine thresholds and to assess perinatal effects associated with isolated maternal hypothyroxinemia identified in the first half of pregnancy.

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 (T(4)) concentrations and thyroid peroxidase antibodies. Women with a free T(4) 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 T(4). Thyroid peroxidase antibody status and the relationship between TSH and free T(4) were analyzed for these women and women with subclinical hypothyroidism.

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 T(4) in normal women (r(s)=-0.19, P<.001) and those with subclinical hypothyroidism (r(s)=-0.11, P=.007). The correlation in women with isolated hypothyroxinemia was not significant.

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 T(4) levels in women with hypothyroxinemia, leading us to question its biological significance.