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 understand 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.
You could also start taking your basal body temperature, to get an idea of your cycle. Although not trying to conceive, I take mine every morning to get an idea on 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.
However, 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. Avoid this at all costs. Get your ducks in a row first.
So what do I do if I fall 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 easily. 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. 
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 6-12 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 child. Some researchers believe that one factor in the development of autism is severe hypothyroidism in their mothers.
Blogger and thyroid advocate Hypothyroid Mom started her site in memory of the baby she lost due to her thyroid levels not being maintained correctly, and fights to stop this from happening to other women and babies.
“Thyroid hormones are essential for the growth and metabolism of the growing fetus. Early in pregnancy the mother supplies her fetus with thyroid hormones. If the mother is hypothyroid, she cannot supply her fetus with enough thyroid hormones. Hence hypothyroidism is a risk factor for pregnancy loss.”
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 good thyroid levels are important. These are generally recommended as a TSH below 2, Free T4 mid-range or a bit higher and a Free T3 in the top quarter of the range,with low antibodies.
You can click on the hyperlinks in the above post to learn more and see references to information given, but more reading and references can also be found at:
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.
Written by Rachel, The Invisible Hypothyroidism
Rachel is a Thyroid Patient Advocate and Expert with Six WEGO Award Nominations, a highly ranked writer appearing in the Top Hypothyroidism Websites and Top Thyroid Websites 2018. Currently studying to become a Life Coach, she has worked with The National Academy of Hypothyroidism, The BBC, The Mighty, Dr. Hedberg, Thyroid UK and ThyroidChange, to name just a few. She is well recognised as a trusted and useful contributor to the thyroid community and has relevant qualifications and certificates in Diet and Nutrition, Reflexology, Motivational Speaking and Positive Thinking.