Hypothyroidism: Fertility & Pregnancy

Hypothyroidism is common and can affect your ability to get pregnant, to stay pregnant and to have a healthy baby. If your doctor or midwife recently diagnosed you with hypothyroidism you are most likely full of questions. In fact, even if you have had hypothyroidism your whole life, you may not know how your diagnosis affects your fertility. What does this diagnosis mean and what can you do? I will explain everything you need to below to help you get pregnant, stay pregnant and have a healthy baby.

For you to understand hypothyroidism I first need to explain how the thyroid hormones function.

There are 3 thyroid hormones.

T4 this is the thyroid hormone produced by the thyroid. Your body then converts T4 into the active form of T3 in your body.

T3– this is the activated form of thyroid hormone used by your body.

TSH– this stands for thyroid stimulating hormone. TSH hormone is produced in the brain. It tells your thyroid to produce more thyroid hormone. So when your thyroid hormone levels (T3 and T4) are low, your TSH is high telling your thyroid to work harder! Conversely when your thyroid hormone levels (T3 and T4) are high, your TSH is low. This tells your thyroid to slow down take a break.

In summary:

Hypothyroid: T3 and T4 are low and TSH is high

Hyperthyroid: T3 and T4 are high and TSH is low.

Anti-thyroid peroxidase (anti-TPO) is another important molecule for you to understand. Anti-TPO is an antibody that attacks your thyroid hormone. If you lab results come back positive for anti-TPO antibody you may have Hashimoto’s disease.

How Does Hypothyroidism Affect Your Chances of Getting Pregnant?

There is some evidence that hypothyroidism may affect your fertility and ability to become pregnant. The assumption is that hypothyroidism impairs your body’s ability to ovulate. In some studies treatment with Synthroid (Levothyroxine) reverses these effects and improves a woman’s fertility. Therefore if you are having difficulty becoming pregnant, ask your doctor or midwife to check your thyroid. Thyroid testing is a routine part of a fertility work-up because of its effect on fertility. With appropriate treatment you should be back on track to achieving your pregnancy.

How Does Hypothyroidism Affect Your Risk of Miscarriage?

The research is mixed. Some studies show no effect of elevated TSH on the risk of miscarriage. Other studies show that elevated TSH increases the risk of miscarriage.

According to one British study from 2014, TSH levels greater than 2.5 were associated with a greater risk of miscarriage. Furthermore TSH levels greater than 4.5 were associated with a 2x risk of miscarriage and TSH levels greater than 10 were associated with a 4x risk of miscarriage. It is generally accepted that the higher the TSH level, the higher the risk of miscarriage. Additionally, + anti-TPO levels further increase your risk of miscarriage. It is important to keep your TSH levels under control. I will explain how to do that later in this article.

How does Hypothyroidism Affect Your Pregnancy?

Research shows that hypothyroidism is associated with elevated pregnancy risks. These risks include preterm delivery, pre-eclampsia and placental abruption. However the risk appears to be greater if the T4 level is low and if anti-TPO antibodies are present. Women who have positive anti-TPO levels are at a higher risk of pregnancy complications than women who are negative for anti-TPO antibodies. The risk appears to be lowest in subclinical hypothyroidism, where only the TSH is elevated. Nevertheless, it is important to receive adequate treatment to normalize your thyroid hormones.

How Does Hypothyroidism Affect Your Baby?

There is speculation that hypothyroidism may affect the cognitive function of children born to hypothyroid mothers. In a 2016 meta-analysis, children born to hypothyroid mothers had a mean intelligence score of 6.27 points lower and a motor score of 5.99 points lower than that of children born to mothers of normal thyroid status. These results are concerning for hypothyroid mothers and put an emphasis on the importance of early and effective treatment of hypothyroidism to mitigate these effects.

Hypothyroidism Screening

If you have no history of thyroid problems, get tested. There is no harm in having your TSH level checked. Although universal screening is currently not recommended, the recommendation is to screen anyone with risk factors. These include anyone who has a history of

  • Difficulty getting pregnant (infertility)
  • Miscarriage
  • Preterm Birth
  • Age >30
  • Symptoms of hypothyroidism (hair loss, fatigue, cold intolerance, weight gain)
  • Family history of thyroid problems
  • Personal history of thyroid problems
  • Type 1 Diabetes

Hypothyroidism Treatment

The medication used to treat hypothyroidism is Synthroid (Levothyroxine). Initial dosing is typically 25-50mcg/day. Consider Treatment if:

  • TSH is >4
  • TSH is >2.5 and difficulty getting pregnant or history of miscarriage
  • +anti-TPO
  • TSH >2.5 and low T4

Dose Adjustment for Pregnancy

If you are treated for hypothyroidism and ttc (trying to conceive) most clinicians recommend keeping your TSH below 2.5. Most women who have achieved normal thyroid (euthyroid) status before becoming pregnant experience an elevated TSH after pregnancy is achieved. One study from 2002 found that 69.5% of women who were previously being treated for hypothyroidism had to increase their dose of Synthroid after becoming pregnant due to an increase in TSH.

This has lead researchers to consider prophylactically increasing the dose of Synthroid when women who were previously receiving treated for hypothyroidism become pregnant.

Women should increase their Synthroid dose by 30%.

In order to increase the dose by 30% women should double their dose 2 days per week. Pregnant women can then check their TSH level every 4 weeks until their TSH level normalizes. In one study, increasing the dose by 30% immediately after pregnancy confirmation significantly decreased the incidence of hypothyroidism in pregnancy.

Therefore if you are being treated for hypothyroidism and trying to conceive, you may want to talk to your doctor about prophylactically increasing your Synthroid dose. You can bring this study with you to show evidence that it is safe and works.

However, another approach is to test TSH upon pregnancy confirmation. Then re-test after 4 weeks and titrate the Synthroid dose according to TSH level. TSH should always be retested 4 weeks after a dose adjustment and at least once per trimester.

How About After Pregnancy?

After pregnancy your provider should decrease your Synthroid dose to your pre-pregnancy dose. The pregnancy that was increasing your need for thyroid hormone has now resolved. However, it is still important that your provider tests your TSH level at your postpartum visit.