The road to pregnancy can be a tough emotional journey as much as it is a physical one. Infertility is a complicated issue, which may have more than just one cause. Certain health conditions like polycystic ovarian syndrome (PCOS) and endometriosis can contribute to infertility, or it may be due to a combination of health factors from both partners. However, people may not realize that thyroid health plays a large role in fertility and reproductive health.
That’s right—the butterfly-shaped organ, at the base of your neck, which releases hormones that help regulate your metabolism, breathing, and body weight, can affect your ability to become pregnant, too.
How thyroid health affects fertility
“Normal thyroid function is essential for fertility and to sustain a healthy pregnancy,” says Elizabeth Milbank, MD, MPH, a board-certified preventive medicine and lifestyle medicine physician who specializes in women’s health at Parsley Health New York.
The thyroid, whose job is to control the body’s metabolism, is a crucial part of the endocrine system and helps regulate male and female sex hormones.
“Undiagnosed and untreated thyroid disease is a common cause of infertility,” says Dr. Milbank. A January 2012 study in the International Journal of Applied & Basic Medical Research shows that the prevalence of hypothyroidism in women of reproductive age is 2 to 4 percent.
Thyroid dysfunction can disrupt a woman’s menstrual cycle, making it more difficult to conceive, interfere with the release of the egg from the ovaries (ovulation), and affect the ability of the uterus to thicken after ovulation, she explains.
Skipped periods, changes in period pattern, heavier periods, and spotting for days prior to the start of a period are signs that there may be a problem with the thyroid, Dr. Milbank says.
However, because other common symptoms of thyroid dysfunction like fatigue, weight gain, and constipation can be subtle and mimic other health conditions, they are often overlooked in young and otherwise healthy women.
With normal function, the pituitary gland produces thyroid-stimulating hormone (TSH) and signals to the thyroid to produce the thyroid hormones, T3 and T4. T4 converts into T3, the active form of the hormone that your body uses. When the thyroid does not make enough hormone, this is called hypothyroidism, or underactive thyroid. Clinical hypothyroidism is diagnosed when you have a high TSH and low T3 and T4 levels. However, subclinical hypothyroidism—an early, mild form of the disease—may occur with or without symptoms and can also affect a woman’s ability to conceive. Subclinical hypothyroidism is characterized by a high TSH but normal thyroid hormone levels.
While hyperthyroidism, or an overactive thyroid, is less common, it can also cause irregular menstrual cycles, which can make it more difficult for women to become pregnant, according to the Office on Women’s Health.
Thyroid hormones have a special relationship with other hormones essential for fertility, such as progesterone, the hormone that prepares the uterus to support a fertilized egg, and estrogen, the hormone that helps stimulate the growth of the egg follicle. These hormones are also crucial during the first trimester of pregnancy because your baby depends on your thyroid hormone supply.
The thyroid’s impact on pregnancy
It’s essential to treat any thyroid disorders before pregnancy, because if left untreated, it can affect fetal development, and may increase the risk for miscarriage, premature birth, and stillbirth In addition, the Endocrine Society says that pregnant women with untreated hypothyroidism are at risk for high blood pressure, anemia, and muscle pain and weakness.
A July 2018 review in the Journal of the Endocrine Society found that in some studies, subclinical hypothyroidism is associated with multiple adverse pregnancy and neonatal outcomes. For example, an October 2014 study in PLoS One showed that pregnant women with subclinical hypothyroidism had an increased risk for gestational hypertension and prelabor rupture of membranes. There was also an increased risk of intrauterine growth restriction and low birth weight.
Just like hypothyroidism, if left untreated, hyperthyroidism can increase the risk of preterm labor and preeclampsia, as well as birth defects and a fast fetal heart rate, the American Thyroid Association reports.
Optimizing thyroid health for fertility and pregnancy
Dr. Milbank says evaluating thyroid health is integral to caring for women who want to get pregnant down the line, are actively trying to conceive, and those who are dealing with infertility, miscarriage, or pregnancy loss. At Parsley Health, Dr. Milbank says doctors will often do a fertility panel, which includes a comprehensive thyroid evaluation, especially for women who have a family history of thyroid disease and a personal history of irregular periods and recurrent miscarriages. It’s also recommended for women who have had trouble conceiving after 6-12 months of trying.
“Women with thyroid disease should be under the care of a physician to determine the best treatment strategy and to monitor thyroid function to ensure that the thyroid hormones are at therapeutic levels. When someone is trying to get pregnant, we typically shoot for a TSH less than 2.5,” Dr. Milbank says.
According to a September 2010 study from The Journal of Clinical Endocrinology & Metabolism, which evaluated the TSH levels of 4,123 pregnant women, those who had TSH levels less than 2.5 during the first trimester had a pregnancy loss rate significantly lower than women who had TSH levels between 2.5 and 5.
“We typically do a comprehensive thyroid evaluation that includes TSH, T3, T4, and thyroid autoimmune testing, such as thyroid peroxidase (TPO) antibodies and thyroglobulin antibodies. The presence of thyroid antibodies doubles the risk of recurrent miscarriage in women with otherwise normal thyroid function,” Dr. Milbank explains.
“We also address lifestyle changes that can optimize fertility, including nutritional strategies, supplements, and stress management strategies.” Elevated cortisol levels can affect thyroid hormone production, so it’s important to also focus on reducing stress in your life.
“I work with my patients on breathwork, meditation, getting regular exercise, and encouraging hobbies, like journaling, gardening, or anything that may bring some sense of peace and relaxation,” Dr. Milbank says.
In addition to getting proper treatment and reducing stress, following a healthy diet packed with vegetables and fruit, limiting gluten, and making sure you get adequate natural sources of iodine, magnesium, and selenium will support thyroid function, Dr. Milbank says.