Hypothyroidism and Pregnancy: Causes, Signs, Symptoms, Diagnosis, Treatment and Consequences

This disease is defined as an underactive thyroid.

This can be from surgical removal, disease, or a congenital problem with the thyroid .

The patient may have been diagnosed during a routine blood test or due to symptoms or complications.

Causes of hypothyroidism in pregnancy

La thyroiditis

Postpartum thyroiditis is an autoimmune disorder that causes thyroid inflammation in the first months after delivery.

It is much more common in women with elevated thyroperoxidase antibodies in the first trimester of pregnancy or immediately after delivery.

It is also more common in women with other autoimmune disorders, such as type I diabetes, and in women with a family history of autoimmune thyroid disease.

Thyroiditis can cause transient thyrotoxicosis due to leakage of preformed thyroid hormone from the damaged thyroid gland into the blood.

As the thyroid gland becomes depleted of preformed thyroid hormone, there is a progression to hypothyroidism before the thyroid gland heals and euthyroidism reestablishes.

In general, only a third of patients with postpartum thyroiditis will experience the classic pattern of triphasic thyroid hormone.

Thyrotoxicosis usually begins 1 to 6 months after delivery, and lasts 1 to 2 months.

A hypothyroid phase may follow, which begins 4-8 months after delivery and lasts 4-6 months.

While 80% of women will regain normal thyroid function within a year, there is a 70% chance of recurrence with subsequent pregnancies in women with a previous episode of postpartum thyroiditis.

Drug-induced hypothyroidism

Other less common causes of hypothyroidism in pregnancy and in the postpartum period include hypothyroidism induced by medications from medications such as amiodarone or lithium.

Signs and symptoms of hypothyroidism

Symptoms of hypothyroidism can include fatigue, difficulty concentrating, intolerance to cold, hoarseness, dry skin, constipation, and weight gain.

It is important to note that not all hypothyroid women are symptomatic.

Also, there is some overlap between the symptoms of hypothyroidism and the symptoms of a normal pregnancy.

Signs of hypothyroidism include dry skin, delayed relaxation of deep tendon reflexes, bradycardia, hoarseness, and non-pitting edema.

Goiter may be present.


There is no universal screening for hypothyroidism in pregnancy.

If there is a family history, symptoms, or other reasons, a blood test to detect thyroid-stimulating hormone levels and free T4 (thyroxine) levels should be reported to the physician.

Key laboratory findings include an increase in the value of thyroid stimulating hormone.

In patients with overt hypothyroidism, the serum free thyroxine level (T4) will decrease, whereas in women with subclinical hypothyroidism, free T4 will be within the trimester-specific reference range.

Thyroid stimulating hormone

A serum thyroid stimulating hormone level is the best and most cost-effective initial test for diagnosing hypothyroidism.

Serum thyroid stimulating hormone will increase in hypothyroid pregnant women.

It is important to note that the normal serum thyroid-stimulating hormone range in the first trimester is lower than in non-pregnant populations.

When trimester-specific laboratory reference ranges are not available, current guidelines recommend that the upper limit for thyroid stimulating hormone be considered 2.5 mIU / L in the first trimester and 3.0 mIU / L in the first trimester. second and third trimesters.

Free thyroxine (T4)

Free T4 values ​​will decrease in women with overt hypothyroidism and normal in women with subclinical hypothyroidism.

As in the case of serum thyroid stimulating hormone, there are physiological alterations in serum thyroid hormone levels throughout pregnancy, so trimester-specific reference intervals should be used optimally.

Additionally, clinicians should be aware that most commercial free T4 trials perform poorly during pregnancy.

Thyroperoxidase antibodies

Thyroperoxidase antibodies can be measured as a marker of thyroid autoimmunity.

Thyroperoxidase antibodies are detectable in most patients with Hashimoto’s thyroiditis.

About 50% of women with detectable thyroperoxidase antibodies in the first trimester of pregnancy will develop postpartum thyroiditis.

Radioactive iodine scans are contraindicated during pregnancy.

The use of 131l is contraindicated during pregnancy and lactation.

If necessary, 123I can be used in breastfeeding women if breast milk is pumped and discarded for several days before resuming breastfeeding.

Management and treatment of the disease in pregnant women

Levothyroxine treatment should be initiated for all pregnant women with serum thyroid stimulating hormone ≥ 10 mIU per liter because overt hypothyroidism in pregnancy has been associated with adverse maternal and fetal outcomes.

It is recommended that levothyroxine be used to treat TPO positive women with serum thyroid stimulating hormone levels> 2.5 mIU per liter.

Levothyroxine can be used to treat TPO-negative pregnant women with serum thyroid stimulating hormone> 2.5 mIU per liter but <10.0 mIU per liter, although there is currently limited evidence of benefit.

Maternal hypothyroxinemia isolated in the context of normal serum thyroid stimulating hormone should not be treated during pregnancy.

The goal of levothyroxine therapy in pregnancy is the normalization of serum thyroid stimulating hormone levels in the trimester: to <2.5 mIU per liter.

Serum thyroid-stimulating hormone levels should be monitored in hypothyroid women at least every 4 weeks until 16 weeks ‘gestation, and then at least once between 26 and 32 weeks’ gestation.

Most women treated for hypothyroidism before pregnancy will require an increase in levothyroxine dose from 25% to 50%.

It should be given to women taking two additional levothyroxine tablets per week, beginning as soon as pregnancy is confirmed.

In most cases, the levothyroxine dose before pregnancy can be resumed immediately after delivery, although it is important to ensure that serum thyroid stimulating hormone has normalized to the post-pregnancy dose at 6 to 8 weeks. after delivery.

Women in the hypothyroid phase of postpartum thyroiditis may not need levothyroxine treatment, as hypothyroidism is usually mild and self-limited.

If hypothyroidism is prolonged, the patient is symptomatic, or if the patient is attempting to become pregnant, L-T4 should be used.

When L-T4 is started, she should be weaned after 6-12 months to determine if thyroid function has normalized.

Many pregnant women take prenatal multivitamins that contain iron or calcium, or take iron tablets for anemia.

Women should be advised to separate their levothyroxine dose by at least four hours from any preparation containing calcium or iron to avoid decreased absorption of levothyroxine.

Postpartum will be another time to look at levels, as medications will most likely need to be adjusted once the baby is born.

This can happen over the course of a few weeks or months and is not necessarily immediately apparent.

Thyroid medications are considered very safe for pregnancy and breastfeeding.

Although they may need to be adjusted regularly during pregnancy and postpartum.

This may mean that your blood tests are done more often than when you are not pregnant.


Hypothyroidism has been associated with adverse obstetric outcomes such as miscarriage, hypertension , placental abruption, preeclampsia , gestational diabetes, low birth weight, preterm delivery, and perinatal and neonatal death.

This study demonstrates that uncontrolled hypothyroidism in pregnant women can have long-term effects on the children of these mothers, it has been associated with decreased intellectual function in children, poor intellectual development, and a lower IQ.

In addition, the effects occur even if the hypothyroidism is mild and the woman does not have any symptoms. However, the more significant the hypothyroidism, the greater the likelihood of developmental problems.

Some women with overt hypothyroidism will also suffer from infertility. Although, in general, if thyroid levels are within normal limits before pregnancy, the risks are greatly reduced. This is why it is important to speak with your doctor before you get pregnant.

Before birth, a baby is completely dependent on the mother for thyroid hormone until the baby’s thyroid gland can begin to function.

This usually doesn’t happen until about 12 weeks gestation (late in the first trimester of pregnancy). Therefore, the mother’s hypothyroidism may play an early role.

In fact, babies of mothers who were hypothyroid early in pregnancy, then properly treated, exhibited slower motor development than babies of normal mothers.

However, during the latter part of pregnancy, hypothyroidism in the mother can also have adverse effects on the baby, making these children more prone to intellectual decline.

Newborns are screened for congenital hypothyroidism. The baby should be evaluated within a few days of being born. There will be a follow-up if the results are inconclusive or if the baby tests positive.

Various medical associations and organizations have made recommendations on screening for thyroid disease.

Some of the recommendations are:

  • All women planning pregnancy should be considered for thyroid disease screening.
  • All pregnant women with a goiter (enlarged thyroid), elevated thyroid antibody levels in the blood, a family history of thyroid disease, or symptoms of hypothyroidism should be tested for hypothyroidism.
  • There is some evidence that antibodies that can contribute to hypothyroidism may play a role in pregnancy. Data suggest that selenium supplementation may be beneficial in women with high antibody levels at preconception.
  • Women who are on thyroid hormone replacement before pregnancy should also be tested to make sure their levels are appropriate.
  • In women with preconception hypothyroidism, most return to their pre-pregnancy thyroid hormone dose within a few weeks or months after delivery.

It should be emphasized that these are only guidelines. The management of each woman’s situation is considered individually after consultation with her physician.

The benefits of treatment extend not only to pregnant women with hypothyroidism, but also to their children.