Fertility and Autoimmune Thyroid Disease: How TSH Alone Isn’t Enough

Until recently, when it came to fertility care, doctors mainly looked at a single marker, TSH, to understand thyroid function. If couples were having trouble conceiving, they could feel reassured that their thyroid and fertilisation chances were fine, as long as TSH levels were within the normal range. 

But reality now lies in recognizing that this holds true only when autoimmune thyroid disease is not at work. Such is the case in India's fertility profile, too. Autoimmune thyroid infertility in India has increased in recent years, indicating not only its high occurrence but also how it sometimes remains undiagnosed until it is too late to prevent infertility in those affected.

Autoimmune thyroid diseases describe a state of health greatly different from primary thyroid hormone deficiency. Autoimmune diseases, such as Hashimoto’s thyroiditis, experience the progression towards illness as a direct result of antibody activity.

Here again, the important feature to keep in mind is that the pathological change begins many years before TSH levels become abnormal. In this period itself, ovulation, implantation, and placental development could be affected.

This is where the limits of TSH become important. The test does not measure immune processes, thyroid hormone tissue availability, or inflammatory load. The presence of a ‘normal’ level of TSH is not in any way indicative of an ongoing autoimmune disorder. Just as importantly, it does not imply that reproduction will occur with maximum effectiveness at this particular hormonal balance. Fertility requires not only a specific but a very specific balance of hormones.

The connection between Hashimoto's and fertility has now been well elucidated in the domain of reproductive health. Infertility among women with autoimmune thyroid disease poses a higher risk of menstrual abnormalities, anovulation, poor response of ovarian reserve, and miscarriage in the absence of hypothyroidism. Autoimmune disease elicits systemic inflammation that disrupts finely tuned events in reproduction.

The challenge is further complicated by the fact that unless patients have a high TSH, thyroid antibodies are rarely checked. This means that people might have to undergo many rounds of fertility treatments without dealing with this underlying driver. In India, with rapid developments in fertility treatments, autoimmune thyroid infertility is underdiagnosed with definite clinical correlations.

The clinical entities of interest for thyroid autoimmunity are:

The connection that people in India might have to Hashimoto is rarely discussed as it may be due to mild symptoms or other factors such as stress or hormonal imbalances.

A fertility-focused thyroid assessment should consist of:

In some cases, reverse/free T3 levels, iodine status, selenium levels, and vitamin D status may also offer helpful information. In order to prepare for assisted reproductive technologies or pregnancy, early detection is especially significant.

The effect of thyroid autoimmunity also extends past conception to include pregnancy. This is because during early pregnancy or the first trimester of pregnancy, the developing fetus solely depends on its mother’s thyroid hormones for neurological development. Autoimmune inflammation disturbs this even before signs of hypothyroidism set in. This is the reason why women with antibodies are more prone to pregnancy loss in early gestation or preterm labor with “acceptable” TSH levels in early pregnancy.

In order to comprehend the Hashimoto's fertility connection clearly, we must also be aware of the fact that not only are these thyroid antibodies signs of disease or illness but also that they contribute to the illness itself. Thyroid antibodies are signs of an underlying tendency toward autoimmunity, and autoimmunity helps explain the persistent increased risk of miscarriage – even when the thyroid function issues are corrected – for these patients.

A full evaluation of thyroid function specifically related to fertility will require more than a reference range for TSH levels. A full screening of free T4, free T3, and thyroid antibodies will provide a more accurate evaluation of thyroid function, particularly as it relates to hormone levels and immune system functioning, a factor often overlooked in thyroid function testing.

This is evident in assisted reproductive technologies, and patients with autoimmune thyroid disease who are subjected to IVF have a higher incidence of implantation failure and early biochemical pregnancies. This implies that patients who do not have autoimmune thyroid disease recognized lead to a conclusion of repeated cycles of assisted reproductive technologies. Therefore, there is a realization of autoimmune thyroid infertility in India.

The connection of Hashimoto's with fertility issues cannot be only a female domain. The thyroid hormone has a documented role in spermatogenesis, sperm count, and seminal hormone concentrations. Couples presenting with unexplained sterility in men with unsuspected or undertreated autoimmune thyroid diseases need to undergo a diagnostic workup on their thyroid status.

Despite the fact that levothyroxine remains the mainstay of hypothyroidism therapy, the management of autoimmune thyroid disease in fertility patients involves various interventions that include:

In India, the incidence of thyroid diseases is high; moreover, the prevailing diseases are related to apparent hypothyroidism in the case of autoimmune thyroid disease. Therefore, the apparent lack of understanding of Autoimmune diseases has led to the failure to identify the disease during critical reproductive periods. In order to address autoimmune thyroid disease and its relation to infertility in India, there is a move away from traditional approaches towards approaches that are proactive and patient-centered. This is particularly true with regard to infertile women and recurrent pregnancy loss.

Generally, people want to ask how it is that the test results show “normal” levels of thyroid function, while they continue to be unable to conceive in their fertility journey. This speaks to the fact that TSH may be useful in diagnosing thyroid failure, but it cannot diagnose it during an autoimmune process in which fertility has already been disrupted. This important fact speaks to why TSH is an inadequate thyroid test by itself in matters pertaining to fertility.

In conclusion, in terms of fertility care, it has to be understood that there cannot be any single score or single result from a diagnostic test that would indicate thyroid health. Autoimmune thyroid disease has to be understood in terms of its complex interplay with fertility. Recognizing autoimmune thyroid infertility in India has to come first in order to be able to tackle what has today perhaps become one of the greatest neglected factors in terms of causing and creating fertility issues.

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1. Can Autoimmune Thyroid Disease Affect Fertility even When TSH Levels are Normal?

Yes. Autoimmune thyroid disease may affect fertility even if TSH levels are within the normal range, as anti-thyroid autoantibodies can affect ovulation, implantation, and early development of the placenta through an unmeasured TSH-mediated inflammatory process itself.

2. Why is TSH by itself not enough for the evaluation of fertility?

While it does monitor the signal to the thyroid, TSH does not monitor thyroid autoimmune disease activity, inflammation, or thyroid hormone supply. Human fertility has higher hormonal control demands than does human health in general. Therefore, the individual who suffers a problem with conception or fetal death should have all thyroid function tested.

3. What thyroid tests should be performed before planning pregnancy?

Other things to consider in addition to the measurement of TSH in the evaluation of the thyroid in the setting of infertility: free T4, free T3, and antibody testing to detect autoimmune disease, such as thyroid peroxidase and thyroglobin antibodies.

4. Does treatment of hypothyroidism completely alleviate fertility problems in Hashimoto’s Thyroiditis?

Not Always. Levothyroxine will correct the hormone deficiency but may not overcome other autoimmune influences that continue to affect fertility as well as pregnancy outcomes. A comprehensive approach is needed for the best possible results.

5. Should thyroid autoimmunity be investigated in unexplained infertility or failure of in vitro fertilization?

Yes. It is an important but often forgotten factor in unexplained infertility, implantation failure, and miscarriages in the first trimester of pregnancy. Its diagnosis and treatment may improve conception and assisted conception methods.

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