If you have been diagnosed with a thyroid condition and are hoping to conceive, it is completely understandable to feel uncertain about what this means for your fertility and your pregnancy. The reassuring reality is that most women with thyroid problems can get pregnant — particularly when their condition is well-managed and their hormone levels are properly controlled. What matters most is not simply whether a thyroid condition is present, but whether it has been identified, treated, and optimised before and during conception.
This guide explains how both an underactive and overactive thyroid can affect fertility, what steps to take when planning a pregnancy, and what to expect once you are pregnant.
How Does Thyroid Disease Affect Fertility?
Thyroid hormones play a fundamental role in reproductive health. They influence the regularity of the menstrual cycle, support healthy ovulation, and help maintain the hormonal environment needed for a fertilised egg to implant and develop. When thyroid function is disrupted — in either direction — these processes can be affected in ways that make conception more difficult.
Hypothyroidism and Fertility
An underactive thyroid is the thyroid condition most commonly linked to fertility difficulties in women. When thyroid hormone levels are low, the body compensates by producing more thyrotropin-releasing hormone (TRH) from the hypothalamus. Elevated TRH can in turn raise prolactin levels — the hormone associated with breastfeeding — which suppresses ovulation even when a woman is not pregnant. The result is irregular or absent periods, anovulatory cycles (where no egg is released), and reduced chances of natural conception.
Research consistently shows that untreated hypothyroidism is associated with a higher rate of miscarriage, particularly in the first trimester. Even subclinical hypothyroidism — where TSH is only mildly elevated and the woman may have no obvious symptoms — has been identified as a risk factor for both reduced fertility and early pregnancy loss. This is precisely why thorough thyroid testing before trying to conceive is so important, not just a standard TSH check.
Hyperthyroidism and Fertility
An overactive thyroid can also affect the menstrual cycle, typically causing lighter, less frequent, or irregular periods — and in some cases stopping them altogether. Uncontrolled hyperthyroidism is associated with a higher risk of complications in pregnancy, including preterm birth and low birth weight. The British Thyroid Foundation advises that, where possible, hyperthyroidism should be brought under control before attempting to conceive.
Thyroid Antibodies and Fertility
Even in women whose TSH and thyroid hormone levels appear normal, the presence of thyroid antibodies — particularly thyroid peroxidase (TPO) antibodies, associated with Hashimoto’s thyroiditis — has been linked to a higher risk of miscarriage and fertility challenges. This is thought to be related to the broader immune dysregulation these antibodies reflect, which may affect implantation and early pregnancy. A comprehensive thyroid panel that includes antibody testing provides a much fuller picture than a basic TSH test alone.
A patient seen at our Birmingham clinic — a woman in her mid-thirties who had experienced two early miscarriages — had been told her thyroid was “fine” based on a single TSH test. When we carried out a full private thyroid blood test including antibody screening, she was found to have elevated TPO antibodies and a TSH sitting at the upper end of the normal range. With appropriate management and careful monitoring, she went on to have a successful pregnancy.
Can You Get Pregnant With an Underactive Thyroid?
Yes — many women with hypothyroidism conceive naturally and go on to have healthy pregnancies. The key is ensuring that thyroid hormone levels are well-controlled before conception and carefully monitored throughout pregnancy.
If you are already taking levothyroxine, it is important to let your GP know you are trying to conceive so that your dosage can be reviewed. Thyroid hormone requirements increase during pregnancy — often by around 25 to 50% — and adjustments typically need to begin as early as the fifth or sixth week of pregnancy. Regular thyroid function tests every six to eight weeks during pregnancy are standard practice to ensure levels remain within the trimester-specific reference ranges.
If you have not yet been diagnosed but are experiencing symptoms of hypothyroidism alongside difficulty conceiving, a private GP consultation is a sensible and straightforward starting point. Identifying and treating even subclinical hypothyroidism before pregnancy can meaningfully reduce the risk of miscarriage and support a healthier conception journey.
Can You Get Pregnant With an Overactive Thyroid?
Conception is possible with hyperthyroidism, but uncontrolled hyperthyroidism carries real risks during pregnancy — for both mother and baby. These include a higher likelihood of preterm birth, low birth weight, pregnancy-induced high blood pressure, and in rare cases, thyroid storm (a sudden, severe worsening of symptoms). For these reasons, most clinical guidelines recommend bringing hyperthyroidism under control before attempting to conceive wherever possible.
Women with Graves’ disease — the most common cause of hyperthyroidism — should be aware that thyroid-stimulating antibodies (TSI or TRAbs) can cross the placenta and potentially affect the developing baby’s thyroid. This is tested for at around 22 to 26 weeks of pregnancy, allowing any necessary monitoring or treatment to be arranged. Women who have previously been treated for Graves’ disease with radioiodine or surgery should discuss their antibody status with their GP before conceiving.
What Should You Do Before Trying to Conceive?
If you have a known thyroid condition and are planning a pregnancy, the following steps will give you the strongest possible foundation:
- Have a comprehensive thyroid function test: This should cover TSH, free T3, free T4, and thyroid antibodies. A basic TSH test alone may not identify all relevant issues.
- Review your medication: If you are on levothyroxine or antithyroid medication, your GP should review your dose in the context of your plans to conceive. Dosage adjustments may be needed before and during early pregnancy.
- Aim for an optimal TSH level: For women planning pregnancy, many clinical guidelines recommend a pre-conception TSH of below 2.5 mIU/L — a tighter target than the general population reference range.
- Address thyroid antibodies: If TPO antibodies are elevated, discuss with your GP whether any additional management or monitoring is appropriate before and during early pregnancy.
- Do not stop medication without guidance: Both levothyroxine and antithyroid drugs should only be altered under medical supervision, particularly when pregnancy is planned or confirmed.
What Happens to Your Thyroid During Pregnancy?
Pregnancy places significant demands on the thyroid. During the first trimester, the developing baby is entirely dependent on thyroid hormones from the mother — its own thyroid gland does not begin functioning until around ten weeks of gestation. The mother’s thyroid must therefore increase its output to meet this additional need. For women whose thyroid is already underperforming, this increased demand can quickly tip them into clinical hypothyroidism if medication is not appropriately adjusted.
Human chorionic gonadotrophin (hCG) — the pregnancy hormone detected in early pregnancy tests — has a mild thyroid-stimulating effect, which can sometimes cause a temporary, minor elevation in thyroid hormone levels in early pregnancy. In most women this is inconsequential, but in those already prone to hyperthyroidism it can occasionally require treatment review.
Postpartum thyroiditis is also worth being aware of. It affects around 1 in 10 women after delivery, causing transient hyperthyroid followed by hypothyroid phases — often in the three to twelve months following birth. It frequently goes unrecognised because its symptoms mirror postnatal fatigue and mood changes. Around 80% of cases resolve within six to nine months, though some women develop permanent hypothyroidism and require long-term treatment.
When to Seek Help
Consider booking a thyroid assessment before trying to conceive if:
- You have a known thyroid condition and have not had a recent medication or hormone level review
- You have been trying to conceive for six months or more without success
- You have experienced one or more early miscarriages
- You have symptoms suggesting thyroid dysfunction — fatigue, weight changes, irregular periods, hair thinning, or anxiety
- You have a personal or family history of thyroid or autoimmune conditions
- You have previously been treated for Graves’ disease
Thyroid conditions are highly manageable with the right care — and addressing them before pregnancy makes a genuine difference to your chances of a healthy conception and pregnancy. At The Private GP, our GMC-registered doctors offer discreet, personalised consultations with same-day appointments available. If you have concerns about how your thyroid might be affecting your fertility, we are here to help you understand your options clearly and act on them promptly. Book a consultation today.
Frequently Asked Questions
- Can hypothyroidism stop you getting pregnant?
Untreated hypothyroidism can make conception more difficult by disrupting ovulation and causing irregular periods, but it does not make pregnancy impossible. Once thyroid hormone levels are properly treated and optimised — ideally with TSH below 2.5 mIU/L before conception — many women with hypothyroidism conceive naturally. Early identification and treatment are the most important factors.
- Should I tell my GP I want to get pregnant if I have a thyroid condition?
Yes — and the sooner, the better. Your GP will want to review your current thyroid hormone levels, check your antibody status if not already done, and ensure your medication is at the right dose for the additional demands pregnancy will place on your thyroid. Ideally this conversation should happen several months before you begin trying, rather than once you are already pregnant.
- Is it safe to take levothyroxine during pregnancy?
Yes. Levothyroxine — the most commonly prescribed treatment for hypothyroidism — is safe to take during pregnancy and is in fact essential for women with hypothyroidism to continue throughout. Stopping or reducing it without medical guidance can pose risks to both mother and baby. Your dose will likely need to be increased during pregnancy and should be monitored closely with regular blood tests.
- Can thyroid antibodies cause miscarriage even if hormone levels are normal?
Research suggests that elevated thyroid antibodies — particularly TPO antibodies — are associated with a higher risk of miscarriage, even when TSH and thyroid hormone levels appear within the normal range. The precise mechanism is not fully understood, but it is thought to relate to broader immune activity rather than hormone levels alone. A comprehensive thyroid panel that includes antibody testing can help identify this risk before it causes further losses.
- How quickly after thyroid treatment can I try to conceive?
For women starting levothyroxine for hypothyroidism, most doctors recommend allowing six to eight weeks for hormone levels to stabilise before trying to conceive, with a follow-up blood test to confirm levels are within the target range. For women with hyperthyroidism, the timeline depends on the treatment used — antithyroid medication generally requires the condition to be controlled before conception, while after radioiodine therapy, most guidelines advise waiting six months before trying. Your GP will advise on the most appropriate timeline for your individual circumstances.