How Thyroid Function Can Impact Ovarian Reserve

For years, we have known that thyroid dysfunction not only impacts fertility but can increase the risk of experiencing miscarriages. This is largely due to the fact that your thyroid is not only involved in your menstrual cycle and ovulation, but it is equally as important for follicular growth, embryo development, implantation and even the formation of the placenta. Thyroid health has also recently been associated with ovarian reserve. Thyroid dysfunction has even been considered as a risk factor associated with reduced ovarian reserve. Although we often think of a patient’s age as the biggest factor associated with a reduction in ovarian reserve, we now know that low ovarian reserve in younger patients could be more associated with dysfunction in thyroid health. So, what does the research say and could addressing thyroid health be a key factor in optimizing your fertility? Let’s dive in. 

Hearing you have low ovarian reserve is something every woman fears. And for good reason, not only is low ovarian reserve associated with low egg count, but the quality of those eggs (oocytes), available for fertilization and ultimately a healthy pregnancy may be significantly reduced. Although new testing, including Anti-Mullerian hormone (AMH) testing can be helpful in evaluating our ovarian reserve, it really is just a guesstimate, at best. Currently, there is no perfect test or imaging study that can truly tell us exactly how many eggs you have left. Although age is considered the most common cause of decreased ovarian reserve, many women in their 20s and 30s may also experience a reduction in ovarian reserve that is not associated with age. Some of the possible causes associated with low ovarian reserve in younger women may include factors like previous pelvic/abdominal surgeries, endometriosis and chemo-radiotherapy. Another more novel factor researchers are learning about is the impact thyroid health has specifically on ovarian reserve. 

Thyroid disease is one of the most common endocrine disorders impacting women in their reproductive years. In fact, it is estimated that women are up to 5-7 times more likely to develop a thyroid condition in their lifetime than men. The other major problem, especially in women in their reproductive years, is that they may be experiencing subclinical hypothyroidism, which may go undiagnosed or untreated for years. Although the “normal” reference range for thyroid stimulating hormone (TSH), is generally between 0.4-4.5 mIU/L for most lab companies, we are now learning that “normal” may not be optimal for fertility and pregnancy. In fact, there is an increased risk of first trimester miscarriages associated with a TSH above 2.5 mIU/L. So although your TSH may look “normal” to your primary care physician, if you are struggling to conceive and have a TSH above 2.5 mIU/L, this may impact your ability to get pregnant. It is also important to remember that although TSH is the most standard thyroid test ordered by most physicians, it is really only one piece of the puzzle. Asking your doctor to evaluate your thyroid hormones including Free T4 and Free T3 as well as thyroid antibodies (anti-TPO and anti-thyroglobulin) is just as important. Researchers have found that even in patients with a “euthyroid” (normal TSH and Free T4) who had elevated thyroid antibodies were not only at an increased risk for miscarriages but they were also less likely to have a successful IVF treatment. So, whether you are trying to conceive naturally or have been told that assisted fertility treatments including IUI and IVF are your best options for a successful pregnancy, addressing your thyroid health has to be a top priority. 

In fact, although there is still so much we need to learn about the direct impact thyroid function has on our reproductive health, studies have shown that many of the cells in the ovaries, including oocytes (eggs), granulosa cells and even the epithelium of the ovaries express receptors for thyroid hormone. TSH, otherwise known as, thyroid stimulating hormone, is the signal that comes from your brain to stimulate your thyroid to make thyroid hormone. It also seems to have a synergistic effect with follicle stimulating hormone (FSH) in promoting the growth of granulosa cells. Granulosa cells are a critical component of the ovary and are essential for the development of eggs, as well as, the production of hormones. 

We also know that reproductive hormones, especially estrogen, can have a significant impact on our thyroid function. In fact, changes in estrogen levels (specifically estradiol) both naturally found in our body, but also synthetically found in birth control and other medications, can increase thyroxine binding globulin. In other words, we may see a reduction in available thyroid hormone when a patient is on estrogen containing medications. It is also the reason that if you are currently on thyroid medication, your doctor may need to adjust your thyroid medication if you recently started estradiol containing medications. This can be common during assisted fertility treatments like IUI and IVF. Although this effect is often temporary, and only occurs while taking additional estrogen, it does speak to the fact that our thyroid and fertility function is very much interconnected. 

Thyroid hormones also play an important role in the process of implantation and early fetal development as it impacts both the endometrial lining as well as the growth of the placenta. Studies have shown that the expression of thyroid hormone receptors in the ovary and endometrium play a critical role in the endometrial receptivity, implantation window, placenta and embryonic tissue. 

Interestingly enough, not only is an optimal TSH and thyroid hormones necessary for improving fertility and ovarian reserve, but autoimmune thyroid disorders (like Hashimoto’s thyroiditis) has been reported to be associated in up to 10-30% of patients with ovarian failure, which again suggests that thyroid function may have a direct role in ovarian reserve. 

So, how can you work on optimizing your fertility and thyroid function to improve your chances of conception? This will, of course, depend on the particular type of thyroid disorder or dysfunction you may be experiencing, as well as additional symptoms. For many women, pharmaceutical intervention, like thyroid replacement, can be extremely valuable. Generally speaking, the most common medical intervention used to treat subclinical and overt hypothyroidism is levothyroxine. Levothyroxine is a thyroid medication that specifically contains T4 to help support an underactive thyroid. Although you may have heard of other more “Bioidentical” thyroid replacement medications like Armour Thyroid, NP Thyroid and previously Naturethroid, the reality is, in terms of fertility support and pregnancy support, Levothyroxine is often the preferred form for most physicians. This comes from the fact that when you are pregnant, especially in your first trimester, your baby will rely solely on your thyroid function and it is thought that if you are consuming a desiccated thyroid replacement medication which may contain both T4 and T3, there may not be enough bioavailable T4 to sustain both your thyroid as well as your baby’s. This isn’t to say that some women aren’t on desiccated T3/T4 formulations but, if you are starting a new thyroid medication and you have been struggling to conceive, chances are Levothyroxine will likely be recommended as a better options for you. 

Slow down On The Iodine

We know that iodine is important and critical for thyroid function but too much iodine can absolutely cause thyroid dysfunction. This is where staying away from “thyroid supporting supplements” and iodine supplements is very important. Aiming for under 100mcg of dietary iodine daily appears to be most effective. Too much iodine can actually drive up thyroid autoantibodies leading to worsening of Hashimoto’s disease. Iodine also lowers Th1 immunity which interferes with autoimmune reactions and can raise inflammatory markers. 

Weight Management 

One of the most common symptoms associated with thyroid disease, especially hypothyroidism,is weight gain. This can be extremely frustrating for patients who feel like they are doing “all the things” to manage their weight but haven’t been successful. But did you know, elevated thyroid antibodies are also associated with higher fasting glucose, insulin levels as well as lipid levels. Making sure you are getting adequate protein, limiting processed fats and simple carbs and making sure to complete moderate (not excessive) exercise are important ways to improve weight management, especially in patients with thyroid disease. If you have struggled with weight loss in the past, additional nutritional support including autoimmune paleo diets may also be beneficial and something to discuss with your doctor. 


You may have heard about the use of inositol for insulin resistance and to stimulate ovulation in patients with PCOS, but did you know that inositol is essential for the communication between your brain and your thyroid gland? In fact, some aspects of this communication depend directly on the presence of inositol. Although inositol does come in dietary forms, generally for those looking to optimize their fertility, as well as, improve their thyroid autoimmunity, additional supplements may likely be necessary. Generally, this will look like an additional 500 mg of inositol per day. Inositol is generally best taken with food and can be taken with other supplements. Always remember that if you are currently on thyroid medication, you will want to make sure to take your thyroid medication on an empty stomach and about an hour away from any other foods, drinks or supplements. Inositol has even been shown to be effective in pregnancy and appears to lower the risk of gestational diabetes in those at risk. 

Although more studies are needed, one interesting study of 48 patients with Hashimoto’s disease were given a supplement containing inositol and selenium. The goal of the study was to see if this supplement could improve thyroid function. Participants were tracked for over six months and were compared to a placebo controlled group. Researchers were pleasantly surprised when they found that participants who took the inositol and selenium supplement not only saw a reduction in TSH levels, by an average of 31%, but their thyroid antibodies improved as well! Researchers found a 42% reduction in Anti- thyroid peroxidase autoantibodies (Anti-TPO) as well as a 42% reduction in anti-thyroglobulin autoantibodies. In fact, roughly half of the participants saw their anti-thyroglobulin levels return back into the normal range! Researchers also evaluated imaging studies of participants and saw improvement in inflammation and nodularity in participants on the selenium and inositol supplement. Our favorite selenium/inositol supplement can be found here. (Please always make sure to consult with your doctor prior to starting a new supplement).


Selenium, similar to inositol, can be found in both dietary and supplemental forms. In fact, even consuming of just 2-4 Brazil nuts per day can be beneficial for thyroid function. Again remember, it’s 2-4 Brazil nuts, not 2-4 servings. Another important way selenium may be used is in supplement form. In fact, there are several human based studies that evaluated the benefit of selenium in specifically lowering thyroid antibodies. In one German study, researchers found that supplementing with selenium for 3 months significantly lowered thyroid antibodies, specifically Anti- TPO. It even improved the appears of thyroid tissue on ultrasound. Another study in France which evaluated over 1800 participants found that supplementing with selenium could reduce the harmful side effects of autoimmunity associated with thyroid disease. Selenium has also been shown to be effective in pregnant women, in fact, one study found that selenium supplementation in pregnant women with selenium deficiency, not only improved thyroid function during pregnancy but postpartum as well.

Although we often discuss autoimmune thyroid disease in terms of Hashimoto’s Thyroiditis, selenium has also been shown to improve autoimmunity of patients suffering from Graves’ disease. In fact, participants with Graves’ disease who took supplemental selenium were seen to respond more quickly to thyroid lowering medications. Generally, selenium is taken at a dosage of about 50mcg per day in addition to the amount available in your prenatal. 

About the Author: Meet Dr. ZenAlissia Zenhausern- Pfeiffer, NMD, FABNE, (commonly known by her patients as Dr. Zen), is a licensed naturopathic doctor board certified in naturopathic endocrinology and the founder of NMD Wellness of Scottsdale, a premier naturopathic medical practice that focuses on helping women to take a proactive approach to their hormone and fertility health. Dr. Zen has been featured as a lead expert in Forbes, Shape Magazine, and Instyle and is deeply passionate about bridging the gap between traditional and natural medicine in the world of fertility. She works with a variety of hormone related issues including PCOS, endometriosis and unexplained infertility. Her goal is to help more women get back into the driver’s seat of their own health to make lasting transformational changes to their health to bring more cute and adorable babies into this world. Read More About Dr. Zen...