Thyroid Disease and Pregnancy


WHAT ARE THE USUAL CHANGES IN THYROID FUNCTION DURING  PREGNANCY?

There are important changes in thyroid functions during pregnancy due to various hormonal changes in the body and usually thyroid gland increases in size by 15%..  Total T4 and Total T3 are not very reliable and hence it is important that tests are performed in reliable labs. At IDEACLINICS we can arrange the appropriate tests required to manage thyroid problems in pregnancy. There is no need to come fasting for thyroid tests, though it is true that thyroid tablets are to be taken on empty stomach. 

WHAT IS THE INTERACTION BETWEEN THE THYROID FUNCTION OF THE MOTHER AND THE BABY?

In the first trimester (i.e. till 12 weeks) of pregnancy, the baby is completely dependent on the mother for thyroid hormone after which the baby’s thyroid begins to produce thyroid hormone on its own. The baby however depends on mother’s iodine consumption which the World Health Organization recommends an  intake of 200 micrograms/day during pregnancy to maintain adequate thyroid hormone production. In India, at present our iodine consumption is similar to the WHO recommendations.

HYPOTHYROIDISM & PREGNANCY

WHAT ARE THE CAUSES OF HYPOTHYROIDISM DURING PREGNANCY?

Hashimoto’s thyroiditis  is the most common cause of hypothyroidism which is due to autoimmune disorder. Approximately, 10% of women will have a slightly elevated TSH of greater than 6 and 1% will have a TSH greater than 10 during pregnancy.

WHAT ARE THE RISKS TO THE MOTHER WITH   HYPOTHYROIDISM?

Though in most situations there may be no symptoms, the possible ones can be anemia, muscle pains (myopathy), pre-eclampsia, heart failure, , low birth weight, placental abnormalities, and postpartum bleeding. These complications can occur in women with severe hypothyroidism while those with mild hypothyroidism this is less likely.

WHAT ARE THE RISKS TO BABY FROM  CONGENITAL HYPOTHYROIDISM ?

Children born with no thyroid function at birth (congenital hypothyroidism) can have severe developmental abnormalities if the condition is not diagnosed and treated promptly. These abnormalities can be completely prevented if the disease is treated immediately after birth. All newborn babies in India should be screened for this preventable cause of mental retardation and at present this screening for congenital hypothyroidism is happening in some cities and towns and not yet made universally available.

WHAT ARE THE RISKS TO BABY FROM  MATERNAL HYPOTHYROIDISM ?

Thyroid hormone is required for brain development in the baby.The effect of mother’s hypothyroidism on the baby’s brain development is not as clear as that of congenital hypothyroidism. However, untreated hypothyroidism in the mother can lead to impaired brain development for the baby. Recent studies suggest that mild brain developmental abnormalities can be present in children born to women who had mild untreated borderline hypothyroidism during pregnancy. As hypothyroidism is common amongst Indians, it has become imperative to screen for this condition before planning pregnancy

IS THYROID TABLET SAFE DURING PREGNANCY?

Thyroid tablet is exactly the same hormone which our thyroid gland produces so its completely safe.

POSTPARTUM THYROIDITIS 

WHAT IS POSTPARTUM THYROIDITIS?

Postpartum thyroiditis is an inflammation of the thyroid that occurs in women after the delivery of a baby causing hyper and or hypothyroidism

WHAT ARE THE SYMPTOMS OF POSTPARTUM THYROIDITIS?

postpartum thyroiditis occurs after the delivery of a baby and thyrotoxicosis occurs first followed by hypothyroidism, so symptoms are those of hyper or hypothyroidism based on the state it is discovered.

WHO IS AT RISK FOR POSTPARTUM THYROIDITIS?

Any woman with:

  • History of previous postpartum thyroiditis (20% )
  • Family history of thyroid problems
  • Autoimmune disorders like Type 1Diabetes or vitiligo)
  • Positive anti-thyroid antibodies
  • History of previous thyroid problems

WHY DO SOME MOTHERS DEVELOP POSTPARTUM THYROIDITIS?

The cause is not known but it is due to an autoimmune disease similar to Hashimoto’s thyroiditis. Anti-thyroid peroxidise antibodies are usually positive similar to Hashimotos’s and is difficult to distinguish the two. Those women with underlying autoimmunity may develop this due to changes in immunity during and after pregnancy.

HOW COMMON IS POSTPARTUM THYROIDITIS?

In India, postpartum thyroiditis occurs in approximately 10% of women. The risk is higher in the following groups.

  • History of previous postpartum thyroiditis (20% of women will have recurrence of thyroiditis with subsequent pregnancies)
  • Family history of thyroid dysfunction
  • Autoimmune disorders (Vitiligo, Type 1 Diabetes Mellitus)
  • Positive anti-thyroid antibodies (higher the antibody higher is the risk)

HOW CAN POSTPARTUM THYROIDITIS AFFECT MOTHERS?

There can be two phases, thyrotoxicosis followed by hypothyroid with over 80% becoming euthyroid within a year spontaneously. However, only a third may have both phases, thyrotoxicosis (happens within four months after delivery and lasts less than three months), this phase is often missed and usual presentation is after four months with features of hypothyroidism lasting for less than a year.

20% of these patients may develop permanent hypothyroidism

HOW IS POSTPARTUM THYROIDITIS TREATED?

Women presenting with thyrotoxicosis may need beta blockers to decrease palpitations and reduce tremors and stopped if symptoms settle. Antithyroid medications donot work in post partum thyroiditis and hence have no role in this form of thyrotoxicosis and any way this phase is transient.

The hypothyroid phase is often treated with thyroid hormone replacement unless patient has asymptomatic mild subclinical hypothyroidism. Treatment ideally is for 6-12 months and then tapered to understand if patient became euthyroid as in atleast over 80% of mothers there will be complete remission.

HYPERTHYROIDISM & PREGNANCY

WHAT ARE THE  CAUSES OF HYPERTHYROIDISM  IN PREGNANCY?

The most common cause (90%) of maternal hyperthyroidism during pregnancy is Graves’ disease and occurs in 1 in 1000 pregnant patients. Sometimes, very high levels of hCG, seen in severe forms of morning sickness (hyperemesis gravidarum), may cause temporary hyperthyroidism.

WHAT ARE THE RISKS TO MOTHER FROM HYPERTHYROIDISM?

Alongside, the usual symptoms of hyperthyroidism, inadequately treated maternal hyperthyroidism can result in early labor ,  pre-eclampsia or rarely, thyroid storm. Graves’ disease generally improves during the third trimester of pregnancy but worsen during the post partum period.

WHAT ARE THE RISKS TO THE BABY FROM  HYPERTHYROID?

There are three possible risks :

  • SEVERE HYPERTHYROIDISM:This can lead to fetal tachycardia, SGA (small for gestational age), prematurity, stillbirths and sometimes congenital malformations.
  • EXTREMELY HIGH LEVELS OF THYROID STIMULATINGIMMUNOGLOBLULINS (TSI):
  • In less than 5% of cases of Graves’ disease in pregnancy, high levels of maternal Thyroid Stimulating Immunoglobulins (TSI), can cause fetal or neonatal hyperthyroidism, these immunoglobulins are typically measured in third trimester.
  • As the antithyroid drugs also cross the placenta, fetal hyperthyroidism is rare. This phenomenon is of a concern for women who are not on anti thyroid drugs and has had prior treatment for Graves’ disease (for example radioactive iodine or surgery).
  • ANTI-THYROID DRUG THERAPY (ATD).
  • Overall, the benefits to the baby of treating a mother with hyperthyroidism during pregnancy outweigh the risks if therapy is carefully monitored. Neither drug appears to increase the general risk of birth defects, however, PTU with less transplacental passage is preferred in first trimester and carbimazole in the later stages of pregnancy. Whichever drug is used, the smallest dose needed is used to avoid fetal hypothyroidism and fetal goitre.

HOW TO  TREAT A PREGNANT WOMAN WITH HYPERTHYROIDISM?

Mild hyperthyroidism usually only needs to be  monitored closely without therapy as long as both the mother and the baby are doing well.

However, severe hyperthyroidism needs treatment with PTU in the first trimester and with Carbimazole in later stages of pregnancy and the aim is to use the lowest doses possible.

Surgical removal of the thyroid gland is only very rarely recommended in the pregnant woman and only when patient is unable to tolerate the anti thyroid drugs.

Radioiodine is contraindicated to treat hyperthyroidism during pregnancy.

CAN THE MOTHER ON ANTI-THYROID DRUGS, BREAST FEED HER INFANT?

PTU is the drug of choice because it is highly protein bound and hence only small  amounts of PTU cross into breast milk compared to Carbimazole.