Hypothyroidism and pregnancy

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1. Overview

Thyroid dysfunction during pregnancy requires special attention because of maternal-fetal complications that can occur in the absence of appropriate treatment. The most common thyroid dysfunction in pregnancy is the hypothyroidism.

Causes that may lead to hypofunction may be iodine deficiency, chronic autoimmune thyroiditis etc.


1. Overview
2. Diagnosis and symptoms
3. Complications
4. Treatment
5. Conclusions

2. Diagnosis and symptoms

Diagnosis of hypothyroidism is established on the basis of some clinical, biochemical and ultrasound criteria.

Clinical manifestations can vary depending on the severity of hypothyroidism:
- Morning asthenia;
- Eyelid edema;
- Dry skin.

In severe forms:
- Mucoid infiltration of the skin and mucous membranes;
- Constipation;
- Hair loss;
- Hoarseness;
- Muscle cramps;
- Impaired memory;
- Decreased intellectual performance;
- Weight gain;
- Decreased heart rate;
- Sometimes an increase in volume of the thyroid gland, also known as “thyroid goiter”.

Biochemically, occur: high TSH with low T4 and T3, anemia, hyperlipidemia.

3. Complications

Severe untreated hypothyroidism during pregnancy can cause birth defects, retardation in fetal development, low birth weight, perinatal mortality and irreversible neurological dysfunction etc. Maternal complications that arise are:
- Miscarriage;
- Detachment of the placenta;
- Premature birth;
- Pregnancy hypertension;
- Preeclampsia and eclampsia.

Because of these multiple possible complications is strongly required a correct and early treatment.

4. Treatment

Hypothyroidism treatment, regardless of its clinic form, is substitutive by administration of thyroid hormone, levothyroxine (LT4). LT4 therapy is essential in women with severe hypothyroidism as those with mild subclinical hypothyroidism (high TSH and FT4 to normal) that have thyroid antibodies (anti TPO).

Besides this, anti TPO during pregnancy, even in patients with normal thyroid function is associated with a significant risk of miscarriage; in these cases the administration of thyroid hormone determines a significant reduction in the rate of abortions, when treatment is administered early in pregnancy.

In women diagnosed during pregnancy with mild subclinical hypothyroidism and in who thyroid antibodies are negative, substitution treatment is still controversial, although there are data to suggest that these cases, left untreated, can cause complications, such as an emerging intellectual coefficient lower in children from these mothers.

Latest recommendations of the American Thyroid Association (ATA) in July 2011, on these cases suggest close monitoring by repeated dosage of TSH and FT4 to capture an eventual progression to severe hypothyroidism.

In patients diagnosed with hypothyroidism before pregnancy would be preferable that, at conception, thyroid function to be normal under treatment. In these women who already receive hormone replacement therapy, the dose is increased by about a third at 4-6 weeks of pregnancy, due to increased thyroid hormone need during pregnancy.

In women diagnosed with hypothyroidism during pregnancy, the treatment should be initiated immediately in order to normalize as quickly as possible the thyroid functional parameters, a normal maternal thyroid function being essential for normal fetal growth and development.

After birth, most women require lower dose LT4. Most of the hypothyroid pregnant women receive food supplements or vitamins that contain iron, this decreasing the absorption of LT4, so it’s important that the two drugs are taken separately, a few hours away, for that hormone therapy be effective.

5. Conclusions

In conclusion, a more careful follow-up thyroid function in pregnant women is very important.

Unfortunately, current guidelines recommend a target dose of TSH screening during the first trimester of pregnancy with or without anti-TPO Ac dosage to women at high risk:
- Personal or family history of thyroid disease;
- Autoimmune diseases;
- Suggestive symptoms of hypothyroidism;
- Recurrent miscarriages, although this strategy may be ignored by between 30-50% of cases with significant thyroid dysfunction.



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