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Preconception screening may identify subclinical hypothyroidism in women
Preconception screening revealed that 1 in 9 women had thyroid function tests consistent with subclinical hypothyroidism, according to recent study findings published in Thyroid.
“Recent data demonstrating both a low median urinary iodine concentration in pregnant women and a high prevalence of subclinical hypothyroidism in the first trimester provided the underlying rationale for the present study,” the researchers wrote.
Alex Stagnaro-Green, MD, MHPE, of the University of Illinois College of Medicine at Rockford, and colleagues evaluated 141 women (mean age, 31.7 years) who presented for preconception screening and counseling to determine thyroid and iodine statuses among them. Researchers evaluated thyroid function tests, thyroid antibodies and urine iodine concentrations among all participants. Thyroid-stimulating hormone levels greater than 3 mIU/L were considered abnormal.
Among all participants, the median TSH level was 1.7 mIU/L with 11% of participants having TSH levels greater than 3 mIU/L when not pregnant. Suppressed TSH levels were not found among any participants. Eight percent of participants were positive for thyroid peroxidase autoantibodies, 15% were positive for thyroglobulin autoantibodies and 16% were positive for at least one of the two.
Participants with detectable antithyroid antibodies had higher median serum TSH concentrations compared with participants who were negative for the antibodies (P = .005). No difference was found for mean free thyroxine levels between antibody-positive and antibody-negative participants. No association was found between miscarriage and the presence of antithyroid antibodies; however, there was a borderline significance for preterm delivery associated with the presence of antithyroid antibodies (P = .07).
Among all participants, the median urinary iodine concentration was 100.5 µg. Forty-seven percent of participants reported taking prenatal vitamins, but the iodine content of the supplements was unknown. No significant difference was found for mean urinary iodine concentrations between participants who did and did not take prenatal vitamins.
No significant relationships were found between urinary iodine concentrations and TSH or free T4.
“In conclusion, the present study reveals marginally adequate iodine nutrition in women presenting to their physician for preconception counseling and a high rate of prepregnancy subclinical hypothyroidism,” the researchers wrote. “The [urinary iodine concentration] findings strengthen the evidence for the mandatory inclusion of iodine in prenatal vitamins in the United States and the importance of beginning prenatal vitamins prior to conception.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.