Prolactin and TSH Screening in Infertility Evaluation
Yes, both prolactin and TSH should be measured in all women undergoing infertility evaluation, with treatment initiated when TSH exceeds 2.5 mIU/L in the preconception period.
Rationale for Universal Screening
While some older data questioned routine screening in asymptomatic women with regular menses 1, the weight of current evidence supports universal thyroid and prolactin assessment because:
- Subclinical disease is common and often asymptomatic - Women with unexplained infertility have significantly higher TSH levels even within the "normal" range compared to controls, with nearly twice as many having TSH ≥2.5 mIU/L 2
- Testing is simple and inexpensive - TSH is a cheap, straightforward screening tool 3
- Treatment is safe, effective, and well-tolerated - Levothyroxine supplementation is easy to apply and carries minimal risk 3
TSH: Measurement and Treatment Thresholds
When to Treat
Initiate levothyroxine when TSH >2.5 mIU/L in women attempting conception 4. This lower threshold (compared to the general population cutoff of 4.0-4.5 mIU/L) is specific to the preconception and early pregnancy period.
The evidence supporting this approach:
- Women with TSH >2.5 mIU/L have impaired fertility outcomes 2
- Treatment reduces infertility duration significantly - from 5.2 ± 1.8 years to 0.5 ± 0.8 years in one cohort 5
- Approximately 54% of hypothyroid infertile women conceived within 6 months of achieving optimal TSH control 5
- In IVF settings, treatment is justified even for TSH >2.5 mIU/L to optimize outcomes 3
Important Caveats
Recent 2026 data suggest that rigid TSH thresholds of 2.5 mIU/L may not universally improve fertility outcomes, with a trend toward higher cutoffs in some contexts 6. However, given the safety profile of levothyroxine and potential benefits, the 2.5 mIU/L threshold remains the most prudent approach in clinical practice 4.
Thyroid Autoimmunity
Check thyroid peroxidase antibodies (TPOAb) alongside TSH. Women with positive TPOAb and TSH >2.5 mIU/L should definitely receive treatment, as they have:
- Increased miscarriage risk 4
- Risk of progression to overt hypothyroidism during ovarian stimulation and pregnancy 7, 8
- Potential for impaired offspring cognitive development 4
Prolactin: Measurement and Treatment
When to Measure
Screen all infertile women with a single prolactin level. While only 1.77% of asymptomatic women with regular cycles have elevated prolactin 1, hyperprolactinemia is a readily treatable cause of infertility that should not be missed.
Critical Pitfall to Avoid
Always check TSH when prolactin is elevated - Primary hypothyroidism can cause severe hyperprolactinemia (levels >300 ng/mL) with normal pituitary imaging 9. Treating the hypothyroidism alone normalizes prolactin without need for dopamine agonists.
Treatment of Hyperprolactinemia
For true hyperprolactinemia (after excluding hypothyroidism):
- Bromocriptine is the preferred agent for women attempting pregnancy, given extensive safety data in >6000 pregnancies with no increased malformation risk 10
- Cabergoline has less published experience but appears safe in limited studies 10
- Discontinue dopamine agonists immediately upon pregnancy confirmation 10
Monitoring During Treatment
Before Conception
- Recheck TSH every 6 weeks until levels are <2.5 mIU/L 5
- Once optimal, follow patients for 6 months while attempting conception 5