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Case-based screening often misses overt thyroid dysfunction in pregnant women
Assessing classic symptoms of hypothyroidism during early pregnancy will not help a clinician detect women at risk for thyroid hypofunction, and case-based screenings should not be used as a risk factor to detect women who require immediate treatment, study data show.
“Pregnant women with severe hypothyroidism cannot be detected during early gestation based on possible symptoms they have,” Victor J. Pop, MD, PhD, professor of primary care at the University of Tilburg in the Netherlands, told Endocrine Today. “These symptoms are nonspecific and include symptoms many pregnant women suffer from during the first trimester, such as fatigue, sleeping problems, poor concentration and low mood.”
Pop and colleagues analyzed data from 2,198 pregnant women without previous thyroid dysfunction participating in the Holistic Approach to Pregnancy and the first Postpartum Year (HAPPY) Project, recruited between January 2013 and September 2014, from 17 community midwife offices in the Netherlands. Women completed questionnaires at 12 weeks’ gestation, including an assessment of “classic” symptoms commonly described to occur in patients with overt hypothyroidism. All participants provided blood samples to measure thyroid-stimulating hormone (TSH), free thyroxine (free T4) and thyroid peroxidase antibodies (TPO-Ab). Women with TSH above the 97.5th percentile and free T4 below the 2.5th percentile were considered to have overt hypothyroidism; those with TSH above the 97.5th percentile and free T4 below within the reference range were considered to have subclinical hypothyroidism. Researchers combined these two categories of thyroid dysfunction, as American Thyroid Association thyroid and pregnancy guidelines call for treating both with thyroid hormone therapy. Researchers compared the prevalence of overt subclinical hypothyroidism between women with high symptom scores and those with low symptom scores.
Within the cohort, 251 women (11.4%) reported thyroid function problems in first-degree relatives at 12 weeks’ gestation; 193 women (8.8) had a TPO-Ab measurement at least 35 kU/L. According to free T4 and TSH cut-offs, there were 15 women with overt hypothyroidism and 68 women with subclinical hypothyroidism.
In assessing hypothyroid symptoms with a 12-item hypothyroid scale, researchers found the mean score was 9.09; women with high hypothyroid symptom scores were defined by at least 1 SD greater than the mean: at least 13.79. In the total sample, 320 (14.6%) of women had high hypothyroid symptom scores; in the total sample of subgroups (2,063 euthyroid women, 15 with overt hypothyroidism and 68 with subclinical hypothyroidism), 302 (14.1%) women had high hypothyroid symptom scores. Of these 302 women, 297 (98.4%) were euthyroid, one woman had overt hypothyroidism and four women had subclinical hypothyroidism. Compared with euthyroid women, the RR of women with high symptom scores to present with overt hypothyroidism was 0.4 (95% CI, 0.05-3.1); the RR of women with high symptom scores to present with subclinical hypothyroidism was 0.36 (95% CI, 0.13-0.98).
“When we — in analogy with commonly used cut-offs in medicine — defined a high symptom score using at least 2 SD greater than the mean as a cutoff (18.49), we found 60 women (2.7%) with high scores,” the researchers wrote. “All of them belonged to the euthyroid reference group — none to the thyroid dysfunction group.”
The researchers additionally noted that during pregnancy, increased levels of estrogens can mask classic symptoms of hypothyroidism, such as brittle hair and dry skin, and serve as a “buffer” against feeling cold, another classic symptom.
“Given that only one of the 15 women who required treatment had symptoms of thyroid disease, one can conclude that the ATA 2017 Thyroid and Pregnancy Guideline recommendation to assess TSH in pregnant women with symptoms of thyroid disease in order to identify women with overt hypothyroidism is not supported by the data of the current study,” the researchers wrote. – by Regina Schaffer
Disclosure: The authors report no relevant financial disclosures.