Thyroid and Fertility: is there a connection?

Welcome back to Fertile Fridays! Today I’m going to talk about the link between thyroid and fertility. While they might not seem closely related, if your thyroid isn’t functioning optimally, it could be a definite hinderance to you getting pregnant and staying pregnant.

The thyroid gland is located in the neck, and is responsible for putting out the thyroid hormone T4, which circulates around the body and is converted to the active form of T3. How much of those hormones it puts out is driven by the pituitary gland sending it TSH (thyroid stimulating hormone), which provides its instruction to produce more. Going even one step further back, it is the hypothalamus that sends the signals to the pituitary to trigger release of TSH.

It all operates on a negative feedback loop, so if there are low levels of T3 and T4 in the body, TSH will actually increase, as it’s telling the thyroid to increase its output. Therefore low thyroid function actually reflects as high TSH (and vice versa).

Both hypo- (low) and hyper- (high) thyroidism have been associated with infertility, however in women of childbearing age, hypothyroidism is far more common, and can go undetected for years. Generally speaking, low thyroid function causes fatigue, easy weight gain, brittle hair and nails, constipation, depression and a host of other symptoms. As it relates to fertility, hypothyroidism can cause irregular menstrual cycles and lack of ovulation. People can have “normal” thyroid labs and still be clinically hypothyroid.

Another important thing to consider when looking at the connection between thyroid and infertility is the possibility of an autoimmune thyroid disease such as Hashimoto’s disease. In Hashimoto’s, there is an initial phase of hyperthyroidism, followed by a fall into hypothyroidism. This is a more common condition than one would think, and can be easily evaluated by lab testing.

Often a primary care doc will run a TSH as a thyroid screen and leave it at that. However, it is so important to get a more comprehensive panel run, especially for purposes of infertility assessment. We must look at all the markers, and we must consider what are “optimal” levels not just “in range” levels. For example, the TSH reference range is 0.35 – 5. In more integrative medical circles it is recognized that 0.35 – 2 is really the ideal range, and that a TSH over 2 may start to indicate sluggish thyroid function. Levels that are on the lower end of the “normal range” of T3 and T4 can also be a red flag, and boosting them up into the middle or upper end of the range can make a world of difference.

Here is the list of labs that I would be asking for:-

• TSH
• Free T3
• Free T4
• Reverse T3 (shows if T4 is converting well to T3 in the body)
• Anti-TPO (checks for autoimmune thyroid)
• Anti-thyroglobulin antibodies (also checks for autoimmune thyroid)

Checking the thyroid is not only important for getting pregnant, but optimizing thyroid health is equally important for staying pregnant and having a healthy baby. There is a higher risk of miscarriage in those with thyroid disorders.

Low thyroid function can be corrected by use of thyroid hormone supplementation. I like the bio-identical one the best, but Armour thyroid and Nature-throid are other options that are typically covered by insurance. The nice thing about those ones is that they contain a combination of T4 and T3, while the pharmaceutical Synthroid contains only T4, and one has to hope that it’s being adequately converted to the active form T3 in the body.

I have taken bio-identical thyroid hormone for years, and it definitely helps my energy and overall well-being. During this time to trying to get pregnant I have increased my dose slightly to push my levels a little higher, while still staying safely within the normal range.

Thyroid health is another piece of the fertility puzzle, so if you haven’t checked it out and you’re struggling to get pregnant, ask your doctor to order those labs and make sure it’s not a limiting factor for you!