Thyroid, prolactin & infertility
TSH in pregnancy, TPOAb, levothyroxine, and hyperprolactinaemia — what the evidence says
Last updated: October 2026 — Sources: Cochrane / EAU / ESHRE / WHO / CDC
Key takeaways
Thyroid disease and prolactin are among the most treatable causes of infertility, but also among the most over-diagnosed. Distinguishing 'a slightly raised test' from 'disease worth treating' determines whether we treat or observe — and that changed after TABLET and the ATA guideline.
TSH ranges shift in pregnancy; non-pregnant ranges do not apply, and universal screening is not recommended.
TABLET (952 women): levothyroxine 50 µg in TPOAb+ women did not improve live birth — 37.4% vs 37.9% (RR 0.97).
Overt hypothyroidism: always treat. Subclinical with positive TPOAb: discuss treatment. Positive TPOAb with normal TSH: do not treat routinely.
Hyperprolactinaemia: one unstressed measurement suffices, dynamic tests are not used, and macroprolactin is checked before imaging.
When to evaluate?
- Infertility or recurrent miscarriage with hypothyroid symptoms, family history or autoimmune disease.
- Amenorrhoea, low libido or galactorrhoea — measure prolactin with TSH.
- Mildly raised TSH (below 10) with positive TPOAb — shared decision, not automatic prescription.
What not to do?
- Do not put every woman trying to conceive on levothyroxine just because TPOAb is positive.
- Do not order MRI for every mildly raised prolactin — check macroprolactin and repeat first.
- Do not use a prolactin stimulation test to diagnose hyperprolactinaemia — not recommended.
Healthcare-professional notice
This hub is independent of NPF products and does not promote them. It is informational only and does not replace individual clinical judgment. Surrogate outcomes (SDF, motility, HOMA, IIEF) are never converted into pregnancy/cure promises, and GRADE certainty is quoted as published.
Binding rule: surrogate outcomes are never converted into patient outcomes. Every certainty grade and limitation is quoted as published.
Deep dive
TSH in pregnancy: range and timing
hCG stimulates the TSH receptor and TSH falls physiologically in the first trimester, hence trimester-specific ranges. Using non-pregnant ranges creates phantom hypothyroidism and exposes pregnancy to unnecessary treatment.
Treatment starts at a dose based on weight and severity, with TSH rechecked every 4 weeks in the first half of pregnancy to adjust the dose.
TPOAb: a marker, not a disease
Antibody positivity indicates autoimmune predisposition but not necessarily thyroid dysfunction. TABLET showed prophylactic treatment in this group does not raise live birth, and serious adverse events were slightly higher in the treatment arm.
Practice: monitor TSH in pregnancy, treat only if it rises, and do not promise that levothyroxine will prevent miscarriage.
Prolactin: from diagnosis to treatment
Prolactin rises with stress, drugs (antipsychotics, antiemetics, some antidepressants) and hypothyroidism. Assessment therefore starts with medication review and TSH before imaging.
Dopamine agonists shrink prolactinomas and restore cycles and pregnancy in most cases, and are stopped once pregnancy is confirmed with clinical follow-up.
Evidence in this domain
Each study broken into five questions: why it was run, who was studied, how it was done, the finding, and why it came out that way — then the clinical takeaway and limits, as published.
FAQ
Does mildly raised TSH prevent pregnancy?
Not definitively. Overt hypothyroidism matters, while evidence for mild elevation is weaker — the decision depends on the value, antibodies and symptoms.
Does high prolactin block ovulation?
Yes, it can suppress GnRH and therefore ovulation and cycles — a common and treatable cause of amenorrhoea with a single drug.
Notice: this reference is informational only and not a substitute for medical advice. Consult your doctor before making any treatment decision.