Stories about our journey, our members, and useful information about fertility.

Hormones 101: Thyroxine (T4) in fertility testing

Thyroxine in fertility – we explain the science.

We want women to be empowered and educated around reproductive health. More of us are choosing to have children later in life. This makes a proactive approach to fertility health important. At Adia, we help women plan ahead and take charge of their fertility journey.

In this blog from our Hormone 101 series, we talk about the link between thyroid hormones, especially T4, in fertility testing. You can read more on thyroid and fertility in our article on Thyroid-Stimulating Hormone (TSH).


What is thyroxine (T4)?

The thyroid is a small, butterfly-shaped gland in your neck producing hormones to regulate metabolism, oxygen usage, hormone levels and energy production. One of these hormones is called thyroxine (T4). When measuring your thyroid function (how well your thyroid works), doctors test your levels of T4, as well as thyroid stimulating hormone (TSH). TSH regulates the production of T4 in your blood. We look at both levels to determine thyroid function.

In our hormone test panel, we’ve included the same thyroid function tests as the NHS, so that’s TSH and T4. We measure the levels of TSH and T4 in your blood with a simple at-home fingerprick blood test.

Why include thyroxine in fertility tests?

A thyroid function test is important if you’ve got low energy levels or symptoms of thyroid disorder. Thyroid function is especially important if you’re trying to conceive. This is because thyroid dysfunction can affect your menstrual cycle, ovulation and ability to conceive. It can also impact the potential effectiveness of IVF.

Having an ‘under-active’ thyroid (hypothyroidism) can lead to higher prolactin levels which can lead to intermittent ovulation, or none at all. Hypothyroidism can also cause ovarian cysts in some women. An ‘over-active’ thyroid (hyperthyroidism) can increase the risk of miscarriage by up to 4 times – so again it’s really important to understand your thyroid function as part of your preconception health plan.

If your thyroid function is less than optimal, the earlier you know, the better. Once you start treatment, the dysfunction is usually corrected and less likely to contribute to fertility problems. Thyroid medication is usually safe to take during pregnancy.

Why do you test for T4 and TSH together?

Testing the level of T4 in your blood alongside TSH determines whether your thyroid is functioning normally. We test both TSH and T4 together for a complete picture of thyroid function. For example, higher levels of TSH but normal levels of T4 may indicate you could be prone to hypothyroidism, but don’t necessarily experience it. High TSH and low T4 can show hypothyroidism, whereas low TSH and high T4 could indicate hyperthyroidism.

Some providers will also test another thyroid hormone: triiodothyronine (T3) after an initial test, if they want to rule out autoimmune thyroid disorders. This is usually only done if such a disorder is suspected.

Can I do anything to keep my thyroid healthy?

Medically speaking, some cases of thyroid dysfunction will be entirely outside of the person’s control. That being said, a healthy diet that supports thyroid function goes a long way. Vitamins and minerals that support thyroid function include selenium, iodine, iron, vitamin A and zinc: these are crucial to healthy thyroid function.

You can learn more about including these vitamins and minerals in your diet by discussing with our Nutrition expert. Simply use the ‘Ask an Expert’ button on your profile to ask a question.

What if my test report indicates abnormal thyroid function?

When you complete a hormone test with Adia, we send you a detailed, personalized report explaining your test results. If anything looks less than optimal, we will let you know. You can discuss this immediately with our expert team, or discuss with your GP.

In any case, please don’t worry – our team of experts is here to help and point you in the right direction. It’s always better to be aware of any imbalance in your hormones because then you can start doing something about it, whether that’s through tackling diet, working on improving emotional health or starting treatment.

Even if everything looks good, and you want to maintain healthy thyroid function, it’s a good idea to discuss your report with our experts.

I hope this explains why we have included T4 in our hormone test panel. For more information on thyroid and fertility, read our article on TSH. If you have questions, please ask our experts!

For more info on thyroid and fertility please contact our experts. Join Adia to ask an expert a question. 

Join Adia

Read other blogs in our ‘Hormones 101’ series: