Thyroid and Fertility

Thyroid problems are extremely common, and because they can be asymptomatic, it can be difficult to know if a condition is present.  We treat thyroid conditions in our Toronto clinic regularly and find it is absolutely essential for healthy fertility.  Dysfunction can cause ovulatory disorders, menstrual irregularity, and recurrent miscarriage.  The thyroid gland is key to support ovarian function. If its function is low, the eggs will not mature fully and, ovulation can be either delayed or prevented.  Surprisingly, 5-20 percent of women in their reproductive years have a thyroid condition.

Autoimmune thyroid disease is one major cause of many thyroid conditions.     Women who test positive for the associated antibodies will generally develop hypothyroidism at a rate of 20% per year.  Often times, when a fertility general health screening is done, the only test completed for the thyroid is TSH (Thyroid Stimulating Hormone).  TSH is a useful test to screen for hypo or hyperthyroidism, however it does not detect autoimmune conditions.  Autoimmune thyroid antibodies can be present with no symptoms of hypothyroidism at all.  In autoimmune thyroiditis, TSH levels are often normal so it is important to complete a full thyroid panel. This can determine if there is a risk of developing hypothyroidism which could threaten a pregnancy.  When a woman becomes pregnant, there are widespread hormonal changes in the body, including an increased demand for thyroid function.   If autoimmune antibodies are present, this can trigger miscarriage due to inability of the thyroid to compensate normally for pregnancy.  Many cases of recurrent miscarriage or premature birth are related to thyroid disease so this is a very important part of fertility screening in those who suffer from miscarriages. One of the protective functions of pregnancy is a decrease in immunity, so it is unlikely that a new flare up of Grave’s disease (an autoimmune disease which causes symptoms of hyperthyroidism and goitre) will occur during pregnancy, however often we see worsening of hypothyroidism.

Another condition which can be present in those with thyroid disease is primary ovarian failure.  This is caused by autoantibodies to the ovary and is associated with autoantibodies to the thyroid.  This condition, although not common, can be devastating for women.

In men, hypo- or hyper- thyroidism can cause poor development of sperm, so for all men with sperm quality concerns, the thyroid should be screened.   Although thyroid disease is more common in women, it can still happen for many men and go undetected.