Guide to hypothyroidism (High TSH) in pregnancy and effects on the baby

Hypothyroidism in pregnancy must be treated correctly to prevent damage to the fetus or worsening in the following months.

Hypothyroidism is an improperly functioning thyroid that does not produce hormones as it should.

When it occurs in pregnancy or the pregnancy already begins in conditions of thyroiditis, it is necessary to introduce or adapt the treatments to avoid damage to the fetus.

So let’s do an in-depth look at this disorder for those who are pregnant.

Normal reference values ​​of TSH in pregnancy

Below are the THS values ​​in pregnancy referred to by the endocrinologist, different from those commonly adopted by the analysis laboratory.

  • First trimester: 0.1-2.5 mIU/L
  • Second trimester: 0.2-3.0 mIU/L
  • Third trimester: 0.3-3.0 mIU/L

First of all we see that normal TSH levels change during pregnancy and therefore the result of the analysis must always be checked against the gestational age.

If you fall within these intervals, you can rest assured . It is clear that minimal variations are not significant (having 3 or 3.3 changes absolutely nothing).

The FT3 and FT4 values ​​are much less reliable in pregnancy for laboratory reasons and generally tend towards low normal values.

Here are the two possible conditions:

SUBCLINICAL HYPOTHYROIDISM : TSH between 3 and 10 mIU/L with normal FT4 values.

This condition causes no harm to the fetus or mother. Despite this, hormone replacement therapy is necessary if not yet started or an adjustment of the therapy already underway. This is to prevent a possible worsening of the hormonal picture in the following months.

CLINICAL HYPOTHYROIDISM : TSH>10 mIU/L with FT4 below normal limits.

This condition can cause harm to the fetus or mother. The sooner it is treated with appropriate HRT, the sooner these possible problems are resolved. So you must never despair!

The damages can be the following:

  • increased risk of premature birth,
  • low birth weight,
  • miscarriage,
  • pre-eclampsia and gestational hypertension,
  • neurocognitive retardation of the child.

The mother with clinical hypothyroidism presents symptoms very similar to those commonly reported during pregnancy:

  • tiredness,
  • muscle weakness,
  • excessive weight gain,
  • dry skin,
  • hair loss,
  • brittle nails,
  • loss of concentration,
  • constipation.

Therefore, in case of doubt, a TSH measurement is the most reliable test.

Iodine intake

Finally, I would like to remind you how important an adequate iodine intake is during pregnancy and breastfeeding (about 250 mcg per day).

Iodine is a trace element found in iodized salt, milk, fish, eggs and to a lesser extent in vegetables. There are also plenty of iodine-containing supplements available for pregnancy.

Severe iodine deficiency during pregnancy can cause:

  • maternal and fetal goiter
  • hypothyroidism
  • increased risk of miscarriage
  • neurocognitive delay in the child

Attention: iodine, on the other hand, must be absolutely avoided in those suffering from hyperthyroidism!

Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.

Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.

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