The Issue of Fertility with Hypothyroidism

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Originally published on 25th Apri1 2017
Last updated on 29th May 2019

Thyroid function and fertility are closely linked.

Abnormal thyroid levels can lead to miscarriage, pre-eclampsia, anaemia, stillbirth and the baby developing congenital hypothyroidism itself, yet many doctors don’t think to check thyroid hormone levels. 

Thyroid hormones directly affect the uterine lining, causing infertility or miscarriages to occur when they are abnormal. As well as complications during pregnancy, some women with low thyroid levels may even struggle to fall pregnant at all.

Hormones TSH (thyroid stimulating hormone) and TRH (thyrotropin-releasing hormone) are ramped up when thyroid hormones such as Free T3 and Free T4 fall too low; TRH to stimulate the pituitary gland to release TSH, which then instructs the thyroid gland to release more thyroid hormones T3 and T4.

Infertility can therefore occur when TRH, which is also responsible for stimulating the pituitary gland to release prolactin, causes the increased prolactin to interfere with the ovulation process, when thyroid hormones are low. The increased prolactin levels (prolactin is also important for promoting lactation) can prevent the ovaries from releasing an egg each month, which makes it more difficult to conceive. I am also noticing more and more women with sex hormone issues such as oestrogen dominance, which can affect cycles and ovulation. Since the thyroid, pituitary and ovaries are all part of the endocrine system, it’s not difficult to see why having problems with one of these, may also mean having issues with another.

Therefore, ensuring your thyroid levels, TSH, Free T3 and Free T4, are all optimal is crucial when trying to conceive, as well as addressing any oestrogen dominance.

You could also start taking your basal body temperature, to get an idea of your cycle. Although currently not trying to conceive myself, I take mine every morning to get an idea of my cycle, seeing as I have a sex hormone imbalance. I am able to tell when I’m ovulating due to a sharp drop and then rise for three days. Knowing if you’re ovulating can not only show you when you have the highest chance of conceiving, but also if you’re actually ovulating and having normal cycles at all. And normal cycles are an indication of overall health as well as thyroid health.

So, I wouldn’t recommend trying to conceive unless you know your thyroid levels are optimal. Not doing so puts the child at risk, but also yourself. I would be concerned about your physical and mental health if you were to go through a complicated pregnancy and/or miscarriage. So try to avoid this at all costs by getting your ducks in a row first.

If you’re ‘subclinical’ or ‘borderline’ hypothyroid, your doctor may wish to start you on thyroid medication or increase it so that you’re well within range to reduce risk of miscarriage. The risk of miscarriage is higher in women with subclinical hypothyroidism, compared to women with normal thyroid function (euthyroidism)[2].

What Do I Do Once Pregnant?

As soon as you know you are pregnant, tell your doctor and get a full thyroid panel booked in as soon as possible. That’s a full thyroid panel. Not just TSH and Free T4. Free T3 and thyroid antibodies too. Make it your mission to look after yourself and your baby as well as possible.

In the first part of pregnancy, the fetus relies completely on the mother to provide the thyroid hormones for its development. For someone with a perfectly health thyroid gland and function, their body is able to meet that extra demand rather easily, but in a woman with hypothyroidism, her body may not be able to.

According to the Endocrine Society’s 2007 Clinical Guidelines for the Management of Thyroid Dysfunction during Pregnancy and Postpartum, thyroid medication usually needs to be increased in dosage, by 4-6 week gestation and may well require a 30-50% increase in dosage. [1]

Most women require an increase in thyroid medication when pregnant, to support the developing baby. Failure to properly maintain adequate thyroid levels whilst pregnant can result in complications such as miscarriage, pre-eclampsia, anaemia, stillbirth and the baby developing congenital hypothyroidism itself. So it’s very important to be tested regularly, often every 4-6 weeks throughout your pregnancy. Adjustments to your medication should then be made accordingly.

It is therefore important to be aware of the effects of low thyroid hormone levels on an unborn child. It’s understood that poor brain development and congenital hypothyroidism can be attributed to poorly managed hypothyroidism during pregnancy, as well as risk of tragically losing the baby. Some researchers believe that one factor in the development of autism is severe hypothyroidism in their mothers.

A recent study also found that among women with diminished ovarian reserve or unexplained infertility, low Free T3 levels and positive thyroid antibodies (TPOAB) are associated with low antral follicle count.

So, as already stressed, maintaining optimal thyroid levels are important.

You can click on the hyperlinks in the above post to learn more and see references to information given.

Book on thyroid disease and pregnancy: Your Healthy Pregnancy with Thyroid Disease: A Guide to Fertility, Pregnancy, and Postpartum Wellness


1. The Endocrine Society. Management of Thyroid Dysfunction During Pregnancy and Postpartum: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism 2007; 92(8)(Supplement):S1-S47.

2. Haixia Liu, Zhongyan Shan, Chenyan Li, Jinyuan Mao, Xiaochen Xie, Weiwei Wang, Chenling Fan, Hong Wang, Hongmei Zhang, Cheng Han, Xinyi Wang, Xin Liu, Yuxin Fan, Suqing Bao, and Weiping Teng, November 2014, Maternal Subclinical Hypothyroidism, Thyroid Autoimmunity, and the Risk of Miscarriage: A Prospective Cohort Study,


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Written by Rachel, The Invisible Hypothyroidism

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One thought on “The Issue of Fertility with Hypothyroidism

  1. If you don’t know how long your cycle is, the date could be inaccurate. This is why a dating-ultrasound may be called for in the early weeks. Those ultrasounds help to confirm approximately how far along you are.

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