Pregnancy Complications and Your Thyroid

Patient Expert
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Healthy thyroid function is crucial to a healthy pregnancy and healthy baby. During the first trimester of pregnancy, a normal thyroid enlarges and increases its output of much-needed thyroid hormone for both mother and baby. Having a pre-existing thyroid condition — or developing thyroid disease during pregnancy — is a risk factor for a variety of pregnancy complications.

Overall, conservative estimates find that maternal thyroid disease occurs in up to 4 percent of all pregnancies, and the actual number may be higher.

Let’s look at some of the specific complications that can result from thyroid disease during pregnancy.

Hypothyroidism and pregnancy complications

The most common thyroid condition seen during pregnancy is hypothyroidism, a lack of sufficient thyroid hormone. Official guidelines of the American Thyroid Association andresearch studies have found that untreated hypothyroidism, inadequately treated hypothyroidism, and subclinical hypothyroidism are associated with an increased risk of many pregnancy complications, including:

  • Miscarriage, also known as spontaneous pregnancy loss

  • Placental abruption, which is the separation of the placenta from the uterus, causing bleeding, contractions, prematurity, fetal distress, and even death to the mother and/or the unborn baby.

  • Gestational hypertension (high blood pressure) and preeclampsia, which occurs at twice the normal rate in women with hypothyroidism

  • Gestational diabetes — a temporary form of diabetes in pregnant women

  • Stillbirth/fetal death

  • Premature rupture of membranes (PROM) and preterm birth at less than 37 weeks of gestation

  • The need for an induced labor

  • Breech presentation, which usually requires surgical cesarean section (C-section) delivery

  • Need for C-section delivery

  • Maternal hemorrhage

  • Heart rhythm irregularities in the fetus, including elevated heart rate (tachycardia) and low heart rate (bradycardia)

  • Lower APGAR score— an assessment of the newborn’s appearance, pulse, grimace, activity, and respiration

  • Low milk supply in the mother, known as hypogalactia

  • Post-partum depression

Compared with women who had no thyroid disease, pregnant women with hypothyroidism are also twice as likely to be admitted to the intensive care unit (ICU) during and after labor and delivery.

Hyperthyroidism and pregnancy complications

Hyperthyroidism — an overactive thyroid — during pregnancy is associated with increased risk of:

  • Miscarriage

  • Preeclampsia

  • Hypertension in pregnancy

  • Stillbirth/fetal death

  • Preterm birth

  • Maternal heart failure

  • The need for an induced labor

  • Fetal growth restriction and low fetal birth weight

  • Fetal tachycardia (high heart rate)

  • Fetal hypothyroidism

  • Fetal hyperthyroidism

Compared with women who had no thyroid disease, pregnant women with hyperthyroidism are also four times as likely to be admitted to the ICU during and after labor and delivery.

Thyroid surgery during pregnancy

In most cases, thyroid surgery is postponed until after your baby is born. But in some cases, if a cancerous tumor is growing rapidly, or a tumor or goiter is impairing your breathing or swallowing, thyroid surgery is performed during pregnancy.

Thyroid surgery during the first trimester increases the risk of risk of miscarriage, and thyroid surgery during the third trimester increases the risk of preterm labor. As a result, surgery is only performed during the second trimester, when it is considered safest for both mother and baby.

Researchers have found, however, that there is a significantly higher rate of post-surgical complications in pregnant women having a thyroidectomy, compared to non-pregnant women. Specifically, there were increased risks for:

  • Hypokalemia (low calcium levels)

  • Laryngeal nerve damage

  • Bleeding

  • Longer hospitalization and recuperation time

It’s important to note, however, that those surgeons who did a high volume of thyroid surgeries had significantly lower complication rates. According to researchers: “It appears to be essential that pregnant patients who require thyroidectomy be directed to high-volume surgeons to optimize their outcomes.”

What should you do?

Some research studies suggest that more careful and thorough thyroid treatment during pregnancy can reduce your risk of complications and adverse outcomes.

Don’t assume, however, that you are receiving sufficient treatment. Research shows that up to 60 percent of hypothyroid women treated with levothyroxine have elevated TSH levels during pregnancy. This is evidence that when you are pregnant, you are at significant risk of going through periods of inadequate treatment.

If you are pregnant and have thyroid disease, it makes sense for you to work with your healthcare provider to ensure that you are receiving the best possible treatment for your thyroid condition.

At a minimum:

  • Insist on frequent thyroid testing during and after your pregnancy.

  • Ensure that all the healthcare providers on your team are aware of your thyroid condition.

See more helpful articles:

Preparing for Pregnancy When Hypothyroid  

Breastfeeding and Thyroid Disease

A Royal Thyroid Problem? Severe Morning Sickness and the Thyroid