Even borderline hypothyroidism, too little of the thyroid hormone, can cause infertility.
The hormones involved in ovulation, fertilization, implantation, and healthy fetal development are similar to musical instruments in an orchestra, says Dr. Roy Weiss, an endocrinology and thyroid expert at the University of Miami Health System and Chair of the Department of Medicine at the Miller School of Medicine. If one of the hormones is missing or out of tune, pregnancy is unlikely to occur.
A recent study by endocrinology researchers has confirmed this cause-effect relationship for women with even mildly low thyroid hormone levels.
“Prior findings taught us that women with very underactive thyroid hormone levels have challenges with fertility,” he says. “This newer study, has shown that less severe hypothyroidism also can negatively affect the ability to conceive. The women enrolled in the research study were evaluated for any other fertility risks and had no known issues. They did not have any history of disease of the thyroid.”
Your thyroid’s role in pregnancy and fetal development
The thyroid gland resembles a small butterfly in shape. It’s located in the neck, in front of the windpipe. When your pituitary gland (an even smaller organ under the brain) releases thyroid-stimulating hormone (TSH), your thyroid secretes two hormones into the bloodstream: thyroxine and triiodothyronine.
“These thyroid hormones help enable other hormones necessary for ovulation,” says Dr. Weiss. “They are equally important to help the baby’s brain and neurological system to develop normally. A human fetus cannot make its own thyroid hormones until into the third month after conception. The baby relies on its mother for these hormones in the early stages.”
Even in less severe cases, subtle deficiency of thyroid hormones can then cause delay in the baby’s development. If the baby’s thyroid gland does not function normally and the mother is deficient in thyroid hormone it can result in a condition known as cretinism, or congenital hypothyroidism. Cretinism can cause Iow IQ, mental retardation, and/or or developmental delays.
Current treatment recommendations
Despite current guidelines, which would have women with mild hypothyroidism treated with thyroid hormone replacement therapy, proper data is lacking, says Dr. Weiss. Additional research is needed to determine if treating the mild hormone imbalance would help such women to conceive.
“Sometimes it is not the thyroid hormones themselves creating infertility,” says Dr. Weiss. “It can be the antibodies that are the underlying cause of the disease. They may interfere with normal thyroid function. Women attempting to conceive could have an autoimmune thyroid disease called Hashimoto’s disease. In this case, the woman’s immune system may be doing more harm than the hypothyroidism.”
The higher the TSH levels, the lower the thyroid hormone levels, he says. It is an inverse relationship. A thyroid hormone tablet treatment would be offered to women who are attempting to conceive and whose TSH levels are greater than 2.0 milli-international units per litre (mIU/L). The study, borderline hypothyroidism was defined as TSH levels of at least 2.5 mIU/L.
John Senall is a contributing writer for UMiami Health News. He is a former hospital and comprehensive cancer center communications director.