Thyroid Disease: What it Means for Your Fertility

Thyroid disease is the second most common endocrine disease affecting women of reproductive age, with a prevalence as high as 7-8%. Many people have known a friend or a family member with thyroid dysfunction affecting their fertility. Many have Thyroid Disease themselves. In addition, with increased awareness of our bodies and overall health, thyroid function is a common cause of concern. However, many people do not realize that the thyroid affects a woman’s reproductive function, including her ability to become pregnant, stay pregnant, and to have a healthy baby.

Classically, Hypothyroidism presents with low blood count (anemia), cold intolerance, fatigue, constipation, hair loss, elevated lipids, delayed reflexes, memory loss, and decreased ability to exercise. Many of these symptoms are general and vague, so to delineate whether the medical cause is Thyroid Disease, a thyroid stimulating hormone (TSH) level should be checked.

Traditionally, Hypothyroidism is defined as a TSH above 5- 10 mIU/L, and a low free T4 (thyroxine hormone). However, studies have shown that the TSH level should be below 2.5 mIU/L in women who are trying to conceive. Well-established causes of hypothyroidism are autoimmune (Hashimoto’s), iodine deficiency, thyroidectomy, inflammation of the thyroid (thyroiditis), medications (iatrogenic), and systemic or psychiatric illness. With such a long list of causes, it is easy to see why thyroid dysfunction can be so common. Unfortunately, this often has a very negative impact on a woman’s fertility and reproductive health.

The Link Between Thyroid Disease, Hypothyroidism, and Infertility

In classic hypothyroidism, a woman has increased risks for infertility and an unhealthy pregnancy. Risks to the pregnancy include miscarriage, low birth weight, premature delivery, congenital hypothyroidism in the newborn (hypothyroidism at birth), preeclampsia, and placental dysfunction.

“Many people do not realize that the thyroid affects a woman’s reproductive function, including her ability to become pregnant, stay pregnant, and to have a healthy baby.”

-Dr. Jennifer Agard, M.D.

Normal thyroid function is crucial to fertility, a healthy pregnancy, and having a healthy baby. Within the last 10 years or so, a lot of attention has been drawn to a condition called subclinical hypothyroidism.

Subclinical hypothyroidism is a condition where a TSH is elevated, however, the thyroid hormones are normal and the person is typically asymptomatic. In 2005, a study found that women with subclinical hypothyroidism were at two times greater risk for preterm delivery, and three times greater risk for a pregnancy complication called placental abruption. Since then, studies over the last few years have shown that in couples being treated for infertility, subclinical hypothyroidism is associated with increased miscarriages and decreased pregnancy rates. So far, the Endocrine Society has been most progressive in addressing subclinical hypothyroidism with recommendations to consider treatment if there are certain risk factors including pregnancy loss.

Finally, TSH is tied to another hormone called prolactin (a hormone that is typically present in breastfeeding moms). Low TSH, can result in increased prolactin. Prolactin is the hormone that stimulates lactation in the breast, allowing for nipple discharge, even in a woman who hasn’t had a baby. Prolactin has a large effect on fertility. It can prevent ovulation of an egg, create irregular menstrual cycles, or even completely prevent menses from occurring.

Managing the thyroid gland is of vital importance as you prepare for pregnancy. Ensuring that you have discussed this with your physician is critical to ensure early recognition and resolution!

Want to learn more about the link between Thyroid Disease, fertility, and your pregnancy health? Please contact Lane Fertility Institute today.



This is a revised article based on “The Thyroid & Fertility: There’s a Link?” by Dr. Jennifer Agard, M.D. in the Spring 2014 Issue of Lane Fertility Magazine.

Author
Dr. Danielle Lane Danielle E Lane, MD, Reproductive Endocrinology and Infertility Specialist

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