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What You Should Know About Thyroid Disease Before You Get Pregnant

The surprising link between your thyroid and fertility problems.

A woman with in a white tanktop and jean shorts sits on a toilet holding a pregnancy test bar in her hand. She stares at it intently.
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If you're having trouble getting—or staying—pregnant, you've likely racked your brain trying to figure out what's going wrong. While it's natural to assume that the problem has something to do with your (or his) baby-making parts, it's possible that another, seemingly unrelated condition is to blame. One option you might not have considered: the health of your thyroid. It might not have crossed your doctor's mind, either.

While fertility specialists frequently screen women for thyroid disorders, don't assume that your regular OB/GYN or internist has taken care of this (unless you've discussed it). "There aren't any universal screening guidelines that say everyone should be screened for thyroid disorders," says Dr. Anita Sadaty, an integrative gynecologist, functional medicine specialist, and attending physician at Northwell Health’s North Shore University Hospital.

That's not necessarily a bad thing—unless it turns out to be the reason why you can't get or stay pregnant.

How the thyroid affects your health and fertility

The thyroid, a butterfly-shaped gland in your neck, is one of those organs you likely don't think much about despite its great power. It makes two hormones, T3 and T4, which control your metabolism. While everyone thinks they'd love to have a fast metabolism, in reality a balance is best: If you secrete too many thyroid hormones (hyperthyroidism), everything speeds up. Yes, it will be easy to lose weight (and hard to gain it) because you're burning up so much energy. But it also means that your heart will beat too fast, you'll breathe too quickly, and you might feel hot all the time. The reverse situation—too few thyroid hormones (hypothyroidism)—is equally problematic. Heart rate and respiration slow down, and it's common to feel cold and sluggish.

Both extremes are bad enough for your own health: hypothyroidism may put you at risk for depression and heart failure, while hyperthyroidism could lead to osteoporosis and heart arrhythmia (irregular heartbeats). Those may be long-term consequences, but if you're trying to have a baby, they matter a lot right now. If you don't have the Goldilocks, just-right amount of thyroid hormones, reproductive hormones in your body can get messed up, too. Your periods might become irregular, and you might not ovulate consistently.

Once you get pregnant, things can also go awry. "There is a clear association between having hypo- or hyperthyroidism and pregnancy complications," says Dr. Sadaty. Pregnant women with thyroid issues are more apt to develop preeclampsia (characterized by dangerously high blood pressure) and give birth to a baby weighing less than 5 pounds. They're also at higher risk for having a miscarriage or stillbirth.

One leading theory about why thyroid problems may have catastrophic consequences in pregnancy is that hormone imbalances might cause the placenta to form or implant abnormally, says Dr. Sadaty.

“There is a clear association between having hypo- or hyperthyroidism and pregnancy complications.”
Dr. Anita Sadaty, OB/GYN

What should you do?

"Anyone who is having trouble getting pregnant or who has had a miscarriage should be screened," she says. Dr. Sadaty’s advice is to look at three different measures of thyroid health. Most doctors who check thyroid function will test your TSH (thyroid stimulating hormone) and free T4 levels. TSH is a hormone made by the pituitary gland in the brain, and it tells the thyroid to make thyroid hormones. A free T4 test tells you how much of this thyroid hormone is actually in your bloodstream.

The third test, a TPO (thyroid peroxidase) antibody test, is not always run, says Dr. Sadaty, but it's important. If you have TPO antibodies, it means that your body is trying to attack enzymes in the thyroid—in other words, that your thyroid disorder is a result of an autoimmune problem. She recommends this test because it's possible to have these antibodies for up to 10 years before you notice any symptoms. That's fine if you aren't trying to have a baby because mild thyroid dysfunction that doesn't cause symptoms usually doesn't need to be treated. But when you're trying to conceive, it's crucial to keep tighter control of your levels.

If you figure out that your thyroid is indeed problematic, treatment can help keep you and your future baby healthy. If you have hypothyroidism, which is significantly more common than hyperthyroidism, you'll need to take synthetic thyroid replacement hormones to make up for what your body is not producing. The catch is that your dose may need to be adjusted during pregnancy. "Your requirements for thyroid hormone can go up 25 to 50 percent when you're pregnant," says Dr. Sadaty. "You'll need to get screened every six to eight weeks, so your doctor can make adjustments."

After you've had a baby, you should also keep your thyroid in mind—even if you never had a thyroid disorder before. "A lot of women develop postpartum thyroiditis, which is when thyroid antibodies go up after childbirth," says Dr. Sadaty. Many times hyper- or hypothyroidism that kicks in for the first time after having a baby resolves in a few months, but if you have any symptoms, it's wise to stay in close touch with your doctor to make sure that your levels bounce back and you don’t need medication.

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Published August 20th, 2019
A young woman with dark curly hair is using mobile phone. Female is smiling while holding smart phone. She is lying on sofa at home.

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