Iodine and pregnancy: why supplement?

Present in large quantities in seawater, iodine is an essential trace element that contributes to normal cognitive function and the normal functioning of the nervous system in adults. Iodine is particularly concentrated in the thyroid gland.

The iodine intake required for a pregnant woman is estimated by ANSES at 200 to 250 micrograms per day, compared to 150 micrograms outside of pregnancy. Several French studies confirm frequent iodine deficiency in pregnant women: a study conducted among 330 pregnant women in the Nice region in the 3rd trimester of pregnancy (Hiéronimus et al., 2009) for example measured a median urinary iodine of 64 µg/L, with a prevalence of deficiency between 74.3 and 85.8% depending on the threshold used (100 or 150 µg/L).

What is the role of iodine during pregnancy?

Iodine is essential for the proper functioning of the thyroid, which uses it to produce its hormones (thyroxine T4 and triiodothyronine T3). In the mother, iodine contributes notably to:

• normal cognitive function;
• normal functioning of the nervous system;
• normal thyroid function and the production of thyroid hormones.

In infants and young children, iodine contributes to normal cognitive development (an assertion currently being evaluated by EFSA, specific to this age group).

According to the WHO, iodine also plays an important role in the neurosensory development of the fetus from the first weeks of pregnancy, a period during which it depends exclusively on its mother's thyroid hormones. Hence the importance of ensuring sufficient maternal intake from the beginning of pregnancy, or even from preconception.

Why do iodine needs increase during pregnancy?

During pregnancy, thyroid gland activity naturally intensifies, and part of the maternal iodine is mobilized by the placenta and amniotic fluid from the second trimester. Certain factors further increase the risk of deficiency:

• twin or multiple pregnancy;
• closely spaced pregnancies;
• a vegetarian or vegan diet;
• known thyroid pathology.

What are the consequences of iodine deficiency or excess?

Severe iodine deficiency can lead to maternal hypothyroidism, characterized by insufficient production of thyroid hormones. The most common symptoms are:

• excessive fatigue;
• weight gain;
• cold sensitivity;
• constipation;
• dry hair and skin;
• memory and concentration problems.

Severe iodine deficiency in the mother can also lead to more pronounced thyroid dysfunction. This is why thyroid function monitoring is part of pregnancy monitoring for women with risk factors.

Conversely, excessive iodine intake can also have harmful effects and lead to congenital hypothyroidism in the newborn. Do not hesitate to consult a healthcare professional, who can prescribe a blood test to assess whether iodine supplementation is necessary. Supplementation should never be decided alone, in either direction.

Where can you find iodine in your diet?

It is recommended to adopt good eating habits before pregnancy, from preconception, to strengthen your iodine reserves.

If your diet is not sufficient to meet your needs, supplementation may be considered. Unlike iron (for which systematic supplementation is not recommended in France), systematic iodine supplementation (around 150 µg/day) is generally recommended from the beginning of pregnancy planning, ideally around three months before conception, and continued during pregnancy and breastfeeding, due to the high frequency of iodine deficiency in pregnant women in France. Talk to your doctor or midwife to determine the dose and form best suited to your situation, especially in cases of known thyroid pathology.

Frequently asked questions about iodine and pregnancy

How much iodine is needed per day during pregnancy?
ANSES recommends 200 to 250 µg per day during pregnancy, compared to 150 µg outside of pregnancy.

Is iodine deficiency common in France?
Yes: several French studies, including one conducted on 330 pregnant women in the Nice region, show that between 74 and 86% of pregnant women have urinary iodine levels below recommended thresholds.

Should I take iodine supplements during pregnancy?
Systematic supplementation (around 150 µg/day) is generally recommended in France from the beginning of pregnancy planning, ideally from 3 months before conception, due to the frequency of deficiency in this population. This should be confirmed with your doctor or midwife.

What are the signs of iodine deficiency?
Excessive fatigue, weight gain, cold sensitivity, constipation, dry skin and hair, memory or concentration problems can suggest hypothyroidism related to iodine deficiency.

Can you take too much iodine during pregnancy?
Yes, an excess of iodine can also be harmful and lead to congenital hypothyroidism in the newborn. Supplementation should always be supervised by a healthcare professional.

This article is for informational purposes only and does not constitute medical advice. Consult your doctor or midwife for personalized advice regarding your iodine intake during pregnancy.