Hypothyroidism and pregnancy

Hypothyroidism and pregnancy

Three situations arise, hypothyroidism before, during and after pregnancy.

The hypothyroidism is manifested by constipation, cramps, weight gain, mood swings, sleep disorders, fatigue, chilliness, dry skin, irregular periods. Outside of pregnancy, it is due to a thyroid surgery, to an iatrogenic cause (by a medication), or after head and neck radiotherapy, due to a central hypothyroidism (pituitary or hypothalamic), or a Hashimoto’s autoimmune thyroiditis.

Before pregnancy, hypothyroidism can affect fertility, making it difficult to get pregnant, or increase the risk of a miscarriage. This is why it is important to diagnose and treat a hypothyroidism before considering a pregnancy. This systematically concerns women with personal or family history of thyroid disorders, women who suffer from an autoimmune disease of any kind, women previously treated for hyperthyroidism. The risk of having a miscarriage is three times greater among women who have antithyroid antibodies than those who do not, even if the thyroid function is normal. The American Thyroid Association recommends maintaining the TSH level below 2.5 mIU/l among women treated for hypothyroidism in the age of procrastination and having a desire of a child.

Hypothyroidism can occur during pregnancy, and is most often due to an autoimmune thyroiditis. Pregnancy is a unique immunological state. There is a reduction in immune phenomenon to accept a child who is 50% genetically foreign to the mother. Thus, while some autoimmune diseases spontaneously see improvement or even remission during pregnancy, others are not influenced or are exacerbated. For women who have autoimmune thyroiditis before conception, pregnancy is usually not associated with improvement or exacerbation of the disease.

Autoimmune thyroiditis may first occur during pregnancy. In this case, many symptoms of hypothyroidism can unfortunately be confused with those of pregnancy and, consequently, the disease will not be diagnosed or treated. Untreated, it may have serious consequences for the mother (increase in risk of miscarriage, hypertension and preeclampsia – formerly called toxemia), and for the baby (retardation of psychomotor development).

When the woman is already treated for hypothyroidism, her needs for thyroid hormone increase from 30 to 50% during the pregnancy, necessitating the adaptation of her treatment according to the levels of TSH, T4 and T3. Monitoring should be regular, every month at the beginning, the goal being the TSH equal or lower to 1 mIU/l. Maternal thyroid hormones pass through the placenta. The thyroid gland of the baby begins to function between the 2nd and 3rd months of gestation. Hormone replacement medication is safe for the fetus, and it will be continued during breastfeeding.

After childbirth, what is called postpartum hypothyroidism concerns 8 to 10% of cases, in women predisposed genetically. It is an auto-immune thyroiditis, and is due to an immune rebound phenomenon. It occurs about 3 to 9 months after childbirth and lasts from 9 to 12 months. 20 % of cases will definitely remain hypothyroidism.
Thus, hypothyroidism is not a reason to avoid getting pregnant. Diagnosed and treated, hypothyroidism allows conceiving and maintenance to term with no problem for the mother and the child, with regular biological monitoring in order to adapt if needed the substitute thyroid hormone.

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