The Thyroid & Fertility; There’s a Link?

By : Jennifer Agard, M.D.

thyroidThyroid 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, or have it themselves. In addition, with increased awareness of our bodies and overall health, thyroid function is a popular 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
exercise tolerance. Many of these symptoms are general and vague, so to delineate whether the cause is the thyroid, 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.

In classic hypothyroidism, a woman has increased risks for 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”

Obviously normal thyroid function is crucial to a healthy pregnancy and a healthy baby. But wait, there’s more. 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 was done on pregnant women with subclinical hypothyroidism and their subsequent children. This 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!


JenniferJennifer Agard, MD, Reproductive Endocrinology and Infertility Specialist. Dr. Agard completed her medical training at UCLA, Saint Barnabas Medical Cen-ter, and Eastern Virginia Medical Center. Her special interests are in polycystic ovarian syndrome, thyroid disease, therapeutic reproductive surgery, and di-minished ovarian reserve. Dr. Agard is committed to the model of delivering individualized patient-centric care. ??er greatest reward is being able to help create the family and life plan that is unique for each of us.