🦋 Thyroid
Thyroid and Fertility — How Thyroid Disease Affects Conception (2026)
Thyroid disorders are a leading cause of fertility problems in women. How hypothyroidism and hyperthyroidism affect fertility and what to do. Updated January 2026.
📅 Updated January 2026⏱ 7 min read👤 Dr. Priya Sharma, MD✓ Medically Reviewed
Key Takeaways
- Even mild subclinical hypothyroidism significantly reduces fertility and increases miscarriage risk
- TSH for conception should ideally be below 2.5 mIU/L — stricter than general normal range
- Hashimoto's antibodies (TPO+) increase miscarriage risk even with normal TSH
- Hyperthyroidism also reduces fertility by disrupting ovulation
- All women planning pregnancy should have thyroid function tested
How the Thyroid Affects Reproduction
Thyroid hormones regulate the menstrual cycle through FSH and LH, affect egg quality and uterine receptivity, and are essential for fetal brain development throughout pregnancy.
2–3×
Higher miscarriage risk with untreated hypothyroidism
2.5
Maximum TSH (mIU/L) when trying to conceive
1 in 8
Women of reproductive age have a thyroid disorder
Hypothyroidism and Fertility
An underactive thyroid disrupts fertility through: anovulation (failure to ovulate), short luteal phase (inadequate progesterone), elevated prolactin (suppressing ovulation), and reduced uterine receptivity. Even subclinical hypothyroidism (TSH above 2.5 with normal T4) is associated with reduced fertility in multiple studies.
Hashimoto's and Miscarriage
TPO antibodies (marker of Hashimoto's) independently increase miscarriage rates even with normal TSH — possibly through effects on placentation or immune tolerance to the embryo. Testing for TPO antibodies is recommended before attempting conception.
Hyperthyroidism and Fertility
Overactive thyroid (Graves' disease) disrupts the HPG axis — elevating sex hormone binding globulin, disrupting LH and FSH ratios, and causing irregular or absent periods. Must be controlled before conception.
ℹ️ Pre-Conception Thyroid Testing
All women planning pregnancy should request: TSH, free T4, and TPO antibodies. Particularly important with: family history of thyroid disease, previous pregnancy loss, irregular periods, difficulty conceiving. Request this specifically — it may not be included in a standard blood panel.
Frequently Asked Questions
What TSH is ideal for getting pregnant?▼
Most fertility specialists recommend TSH below 2.5 mIU/L when trying to conceive — stricter than the broad 'normal' range of 0.4–4.0. Women with Hashimoto's or previous miscarriage should aim for below 2.0. Discuss levothyroxine with your doctor if TSH is above 2.5.
Can I get pregnant with hypothyroidism?▼
Yes — many women with well-managed hypothyroidism conceive normally. The key is optimising thyroid levels before conception. Uncontrolled hypothyroidism significantly reduces fertility through effects on ovulation. With treatment, fertility is usually restored.
Does Hashimoto's cause miscarriage even with normal TSH?▼
Yes — women with TPO antibodies have 2–4× higher miscarriage rates even with normal TSH. Some evidence suggests levothyroxine treatment reduces miscarriage risk in TPO-positive women, though not yet universally recommended.
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⚕️ Medical Disclaimer: For informational purposes only. Not a substitute for professional medical advice. Always consult a qualified healthcare professional.
PS
Dr. Priya Sharma, MD
WellCalc Medical Contributor
All WellCalc articles are reviewed by qualified healthcare professionals following NHS, AHA, and WHO guidelines.