Getting pregnant when you have a thyroid problem

Written by: Dr Mark Vanderpump
Edited by: Bronwen Griffiths

There are many variables that contribute to pregnancy occurring, but did you know that an untreated thyroid problem could affect a number of these? Dr Mark Vanderpump, a top endocrinologist, explains the role that the thyroid gland plays in fertility and why thyroid problems must be treated.

What role does the thyroid play in fertility?

Conception is surprisingly tricky given the many ways in which the body’s functions must be perfectly aligned in a small window of time. This includes the facts that:

  • Your ovulation cycle must be regular.
  • Your body temperature cannot be too low.
  • Your fertilised eggs must be securely implanted and given time to develop.

All of these things can be negatively affected by an untreated thyroid problem.

An underactive thyroid can produce low levels of thyroxine (T4) and high levels of thyroid stimulating hormone (TSH). This stimulates an overproduction of prolactin, which disrupts the ovulation cycle.

You may also stop ovulating completely if poor thyroid levels disrupt the ability of luteinising hormone (LH) to stimulate your ovary to release an egg. Since it’s still possible to menstruate despite this problem, this situation is not necessarily obvious.

If your periods are heavy, light or infrequent, this can be due to either an underactive or overactive thyroid and, of course, this can be problematic for conception.

An underactive thyroid can also cause your body temperature to drop, which makes it difficult for cell division to take place, and it can shorten what is known as the luteal phase. This is the second half of the menstrual cycle and needs to be 13 to 15 days long in order to nurture any fertilised eggs.

Read more: thyroid problems

I’m struggling to conceive and have a thyroid problem, what should I do?

Firstly, you should ask your doctor to check your thyroid if:

  • There is a family history of thyroid problems.
  • You have an irregular menstrual cycle.
  • You have been trying to conceive without success for more than 12 months.
  • You have a noticeably enlarged thyroid.

If you are then told you have a thyroid condition or if you have already been diagnosed with an underactive or overactive thyroid, there is no reason that you shouldn’t have a healthy pregnancy and baby.

However, in advance of trying for a baby, it’s important to work with your doctor in order to optimise your outcomes, both before and during pregnancy. It is usually recommended that your TSH level should be kept in the lower half of the reference range (between 0.5 and 2.5 mU/L).

As the baby’s healthy brain development is very much dependent on the mother’s thyroid hormones during the first trimester, your GP and/or midwifery team will want to closely monitor your ongoing levels. Your medication may need to be adjusted in order to mimic the body’s natural increase in the production of thyroid hormones by up to 50%.

What happens if I have an underactive thyroid?

It is perfectly safe to continue taking levothyroxine, the synthetic form of thyroxine, during pregnancy, and it is usual for your dose to be increased by between 25 and 50 mcg soon after the pregnancy is confirmed.

If you have been additionally prescribed supplements like iron or calcium you should wait at least an hour before taking levothyroxine as these may affect its absorption.

If you are experiencing morning sickness, you will need to change the time you take your levothyroxine to ensure its full effect. Taking it last thing at night is also acceptable.

What happens if I have an overactive thyroid?

If you have had radioiodine treatment for Graves’ disease it is recommended that you wait six months before trying for a baby. If your male partner has had treatment in the same way, he must wait four months before fathering a child.

You will be measured for Graves’ disease antibodies early in your pregnancy as these can cross the placenta and cause temporary symptoms of thyroid overactivity in the baby during the second half of the pregnancy and for up to three months post birth.

Read more: Grave's disease


If you experience severe nausea and vomiting such that you are losing weight and experiencing dehydration, you must go to the doctor. This can be a sign of excessive levels of a hormone called hCG which can lead to a temporary form of hyperthyroidism that appears only in the first half of the pregnancy (gestational thyrotoxicosis).

Can thyroid conditions cause problems in pregnancy?

I cannot stress enough that it is vital to visit your GP if you have a suspicion that you might get/already have a thyroid problem. Lack of treatment if you are either hypothyroid or hyperthyroid may cause problems for both the mother and child. Pregnant women with severe thyroid disease can experience:

In summary, the diagnosis of a thyroid condition does not automatically mean problems with conception, pregnancy, labour or the arrival of a healthy baby, provided that you liaise closely with your doctors and midwives.

By Dr Mark Vanderpump
Endocrinology, diabetes & metabolism

Dr Mark Vanderpump is a highly experienced consultant endocrinologist based in London who specialises in adrenal gland disorders, hyperparathyroidism and hyperthyroidism alongside hypothyroidism, thyroid disorders and diabetes. Furthermore he has significant expertise in treating polycystic ovaries (PCOS). He practices at The Physicians' Clinic, Wellington Diagnostics & Outpatients Centre and One Welbeck Digestive Health clinic.

Dr Vanderpump has had a career spanning over 30 years, and was previously a consultant physician and honorary senior lecturer in endocrinology and diabetes at the Royal Free London NHS Foundation Trust. His main area of expertise is thyroid disease, but his clinical practice includes all aspects of diabetes and endocrinology. He also sees referrals of less frequently-occurring conditions such as thyroid cancer; pituitary conditions such as acromegaly; and adrenal disorders including Addison's disease, plus calcium and bone disorders.

Dr Vanderpump, who is highly qualified with an MBChB, MRCP and MD alongside a CCST and FRCP, did higher training in the West Midlands, North East England and North Staffordshire.

Dr Vanderpump is a respected figurehead in the endocrinology community. He is the former president of the British Thyroid Association and former chair of the London Consultants' Association.

He continues to lecture on diabetes and thyroid disease, is widely published in peer-reviewed journals and has published a book called Thyroid Disease (The Facts). He is also a member of the Royal College of Physicians (RCP), where he is also a fellow, the British Thyroid Association (BTA) and the Society of Endocrinology (SoE). Furthermore, he has professional membership of the Association of British Clinical Diabetologists (ABCD) , London Consultants' Association and the Independent Doctors Federation.   

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