How Iodine Deficiency Affects Thyroid Function During Pregnancy

Iodine (I2) moleculeIf a woman is iodine deficient during pregnancy, it may have an adverse effect on her baby.  However, iodine deficiency (ID) is still common in Europe.

A studied published online on April 2, 2012, ahead of appearing in print in the journal Thyroid examined the iodine levels and thyroid function of pregnant French women in Lyon.  The article is “Pregnant French Women Living in the Lyon Area Are Iodine Deficient and Have Elevated Serum Thyroglobulin Concentrations.”

This was a cross-sectional study that used healthy pregnant women who did not have a history of thyroid disease; there were 228 women in the study, and they were consecutively recruited from an obstetric clinic.  They represented all trimesters.

The researchers measured the following in the women:  thyrotropin (TSH), free thyroixine (FT4), anti-thyroid peroxidase antibodies(anti-TPO), thyroglobulin (Tg), and urinary iodine concentration (UIC) (n=100).  Non-pregnant adults were used as the controls, and their thyroid function was compared to the subjects’ thyroid function.

For the UIC, the median (range) was 81 (8-832) μg/L.  Seventy-seven percent of the subjects had a UIC level < 150 μg/L, which means that they had an inadequate iodine intake.  UIC was not a significant predictor for the thyroid function tests when controlling for maternal age and stage of gestation.

Looking at thyroid hormone levels, 11% of the pregnant women had abnormal TSH or anti-TPO levels.  At first, second, and third trimesters, median FT4 was 14.9, 12.6, and 11.5 pmol/L, respectively. However, Tg levels in pregnant women was not different throughout the trimesters; the median was 16.2 μg/L, which was significantly higher than the Tg median in the non-pregnant women (11.7 μg/L) (p = 0.02).

French women living in the Lyon metropolitan area are iodine deficient, and when compared to non-pregnant women, have higher Tg concentrations.  Most likely this elevation during pregnancy is because of thyroid hyperstimulation exacerbated by iodine deficiency.

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