Thyroglobulin a good indicator of iodine status in pregnancy

In pregnant women, serum thyroglobulin (Tg) levels correlate well with urinary iodine concentration (UIC) and iodine-to-creatinine ratio (ICR), and may be a good marker for iodine status, a recent study has found.

The study included 241 pregnant women (mean age 30.3 years) in whom serum Tg levels were measured at each trimester using electrochemiluminescence assays. At each visit, a random nonfasting spot urine sample was collected for UIC measurement and ICR calculation.

The median baseline UIC was 73 µg/L, less than half of the WHO recommendation of a 150-µg/L cutoff. On this basis, researchers deemed the current cohort to be iodine deficient. Median UIC during the first, second, and third trimesters of pregnancy were likewise low at 73, 94, and 117 µg/L, respectively. Corresponding ICRs at each trimester were 116, 147, and 150 µg/g.

After excluding 15 participants who were positive for Tg antibodies, a total of 473 samples were subjected to the immunoassay, yielding a median Tg of 17 µg/L. Of note, 12.5 percent of participants had Tg ≥44 µg/L. Median Tg during the first, second, and third trimesters were 19, 16, and 16 µg/L.

Researchers also found that Tg was significantly and negatively correlated with UIC (r, –0.262; p<0.001), ICR (r, –0.147; p<0.01), and thyroid-stimulating hormone (TSH; r, –0.134; p<0.01).

During the first trimester of pregnancy, Tg remained negatively associated with UIC (r, –0.258; p<0.001), urinary ICR (r, –0.277; p=0.002), and TSH (r, –0.147; p<0.05), and positively correlated with free T4 (r, 0.178; p<0.05). By the second trimester, only UIC (r, –0.217; p<0.05) and ICR (r, –0.280; p<0.01) were associated with Tg. No such interactions were detected during the third trimester.