Iodine and pregnancy: why supplement?

Present in large quantities in seawater, iodine is an essential trace element that contributes in particular 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 by a pregnant woman is estimated at 200 to 250 micrograms per day by ANSES, compared to 150 micrograms outside of pregnancy. Several French studies confirm frequent iodine deficiency among pregnant women: a study conducted on 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 ranging from 74.3% to 85.8% depending on the threshold used (100 or 150 µg/L).

What is the role of iodine during pregnancy?

Iodine is essential for normal thyroid function, which uses it to produce its hormones (thyroxine T4 and triiodothyronine T3). In the mother, iodine contributes specifically to:

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

In infants and young children, iodine contributes to normal cognitive development (a claim 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 pre-conception.

Why iodine requirements increase during pregnancy

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

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

What are the consequences of an 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;
• sensitivity to cold;
• constipation;
• dry hair and skin;
• memory and concentration problems.

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

Conversely, excessive iodine intake can also have harmful effects and cause congenital hypothyroidism in the newborn. Therefore, do not hesitate to consult a healthcare professional, who can prescribe a blood test to evaluate whether iodine supplementation is necessary. Supplementation should never be decided on your own, in either direction.

Where can you find iodine in your diet?

It is recommended to adopt good eating habits before pregnancy, from the pre-conception stage, to build up your iodine stores.

If your diet is not enough to cover 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 point of planning a pregnancy, ideally about three months before conception, and continued during pregnancy and breastfeeding, due to the high frequency of iodine deficiency among pregnant women in France. Talk to your doctor or midwife to determine the dose and form best suited to your situation, especially in the case of a known thyroid condition.

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 the recommended thresholds.

Should I take iodine supplements during pregnancy?
Systematic supplementation (about 150 µg/day) is generally recommended in France as soon as a pregnancy is planned, ideally 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, sensitivity to cold, constipation, dry skin and hair, memory or concentration problems may suggest hypothyroidism linked 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 must always be supervised by a healthcare professional.

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