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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.
This article looks at how fertility can be affected with thyroid disease and what we can do about it.
How Low Thyroid Hormone Levels Can Cause Infertility
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.
Where Can I Order Fertility Testing?
Ways To Maximise Your Fertility
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. I wouldn’t recommend trying to conceive unless you know your thyroid levels are optimal and you have your ducks in a row first. Not doing so puts the child at risk, but also your own mental health. 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).
See related post: Are Pregnant Women With Thyroid Problems Considered High Risk?
You could also start taking your basal body temperature, using a BBT thermometer, to get an idea of your cycle. Even when I wasn’t trying to conceive, I took my BBT every morning to get an idea of my cycle, when I had sex hormone imbalance. I was able to tell when I was ovulating due to a sharp drop in my temperature and then rise for three days. Addressing any oestrogen dominance should be of importance also.
Knowing if you are 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.
I personally wasn’t ovulating for a year or so, due to oestrogen dominance. By working with a functional medicine practitioner and going gluten-free, this quickly resolved however.
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. 
Feel free to share your experiences in the comments section below.
You can click on the hyperlinks in the above post to learn more and see references to information given.
You, Me and Hypothyroidism: When Someone You Love Has Hypothyroidism, a book for those who know someone with hypothyroidism. It looks at how parenting, fertility, home life and more can all be affected by hypothyroidism, and what you can do about it.
A book on thyroid disease and pregnancy: Your Healthy Pregnancy with Thyroid Disease: A Guide to Fertility, Pregnancy, and Postpartum Wellness
Rachel Hill is the highly ranked and award-winning thyroid patient advocate, writer, blogger, speaker and author behind The Invisible Hypothyroidism. She has two books: ‘Be Your Own Thyroid Advocate‘ and ‘You, Me and Hypothyroidism‘. Her thyroid advocacy work includes authoring books, writing articles, blogging and speaking on podcasts. Rachel has worked with The National Academy of Hypothyroidism, BBC, The Mighty, Yahoo, MSN, ThyroidChange and more. She is well-recognised as a useful contributor to the thyroid community and has received eight 2020 WEGO Health Award Nominations.