Endocrine Abstracts

Serum thyroglobulin (Tg) is a biomarker used to assess iodine nutrition status, but data in pregnant women are scarce.

Objectives: To determine serum Tg concentration in Spanish healthy pregnant women, and to evaluate its relation with yoduria (UIC), thyroid volume, iodine intake and thyroid function throughout pregnancy.

Methods: Longitudinal study in pregnant women with no history of thyroid disease, recruited in 2 obstetric centers of Pamplona (Spain) at the first antenatal visit. We performed anamnesis, iodine intake questionnaire, thyroid ultrasound, and UIC in a single visit. Thyrotropin (TSH), free thyroxine (fT4), antiperoxidase and antithyroglobulin (anti-Tg) antibodies were determined in the three trimesters, and Tg in the first and third trimesters. We compared Tg concentrations in women according to the consumption of iodized salt, milk intake and pharmacological iodine supplements.

Results: We evaluated 100 pregnant women in the 10th gestational week, 92% Caucasian. To establish thyroglobulin values we excluded multiple pregnancies (n=2), women with positive anti-Tg antibodies (n=14) and/or nodular goiter (n=2), leaving a population of 82 women. The median Tg was 14.1 μg/l. Only 1 woman had Tg> 40 μg/l (Tg 42.3 μg/l in the third trimester). Tg at 9th gestational week (n=65) was lower compared with Tg at 37th gestational week (n=20): 12.4 vs 22.8 μg/l; P<0.001. Women with anti-Tg antibodies had lower Tg values than those with negative antibodies (Tg 6.44 vs 14.1 μg/l; P=0.007). Five of the 14 women (35.7%) with positive anti-Tg antibodies, had undetectable Tg concentrations (<0.2 μg/l). The median yoduria was 251 μg/l (188.5-368.5). No correlations between serum Tg concentrations and UIC, thyroid volume, TSH or T4l concentrations were found. Women who started iodine supplementation (200 μg/daily) at least 1 month before pregnancy, had lower median Tg, compared to those who started at the detection of pregnancy, and those with no iodine supplementation (Tg 10.8 μ/l vs 13.4 μ/l vs 23.4 μg/l respectively; P=0.030). We found no statistical differences in Tg concentrations according to the consumption of iodized salt (no consumption, since pregnancy detection or pre-pregnancy) or according to milk intake (<1, 1–3 or >3 daily servings).

Conclusions: In our population serum Tg does not correlate with yoduria, thyroid volume, thyroid function, use of iodized salt or milk intake. Starting iodine supplements at least 1 month before pregnancy is associated with lower Tg.