Thyroid, prolactin & fertility
The thyroid and prolactin are two hormonal “players” that often, and quietly, affect fertility. Their disorders can disturb ovulation or influence the course of a pregnancy — and, fortunately, are often treated simply.
At the same time, there is overuse around these tests: not every borderline value needs treatment. Correct, evidence-based interpretation is what matters.
How does the thyroid affect fertility?
The thyroid regulates metabolism and works closely with the reproductive system. Overt (clinical) hypothyroidism can disrupt ovulation, cause irregular periods and increase the risk of miscarriage; that is why it should always be corrected before trying to conceive.
Testing is done mainly by measuring TSH (thyroid-stimulating hormone). In women with symptoms of thyroid disease or menstrual disturbances, thyroid testing is part of the basic assessment.
What is subclinical hypothyroidism and does it need treatment?
Subclinical hypothyroidism is the situation where TSH is mildly raised while thyroid hormones remain normal. Here the data are more nuanced: for a mild rise in TSH (about 2.5–4.0 mU/L), randomized trials have not shown a clear benefit of levothyroxine on birth rates.
A possible benefit seems more likely when TSH is clearly raised (above 4.0 mU/L). The treatment decision is individualized, taking into account the exact value, the antibodies and the history — not mechanically every borderline measurement.
Do thyroid antibodies play a role?
Antibodies against thyroid peroxidase (anti-TPO) indicate autoimmune thyroiditis and are linked to a slightly increased risk of miscarriage. In the past, many doctors gave levothyroxine to these women, even when the thyroid was working normally.
Two large randomized trials, TABLET and T4LIFE, showed that levothyroxine in euthyroid women with positive anti-TPO does not increase births or reduce miscarriages. So preventive treatment in these cases is no longer recommended as routine.
What is raised prolactin (hyperprolactinaemia)?
Prolactin is the hormone associated with breastfeeding. When it is excessively raised outside pregnancy, it can suppress ovulation and cause irregular or absent periods and, sometimes, milk discharge from the breasts.
Causes include benign pituitary tumours (prolactinomas), certain medications, hypothyroidism and stress. That is why a raised value is confirmed by repeating it and investigated before being attributed to a specific cause.
How is raised prolactin treated?
When hyperprolactinaemia causes ovulatory disturbance and infertility, it is treated very effectively with medicines called dopamine agonists (most often cabergoline). These lower prolactin and restore ovulation in the great majority of women.
Treatment is not always needed: a mild, asymptomatic rise without an effect on the period can simply be monitored. The aim is to treat the problem when it genuinely blocks fertility — not every number.
What is the practical takeaway for couples?
Testing the thyroid and prolactin has a place mainly when there are symptoms or a menstrual disturbance, and it is a simple, inexpensive part of the assessment. Overt hypothyroidism and symptomatic hyperprolactinaemia should be corrected.
At the same time, not every borderline value needs treatment. Mild deviations — subclinical hypothyroidism with a low TSH, positive antibodies with a normal thyroid — are assessed on the evidence, not by automatic prescription.
Summary
The thyroid and prolactin affect ovulation and pregnancy. Overt hypothyroidism and symptomatic hyperprolactinaemia (with dopamine agonists such as cabergoline) should be treated. But mild deviations call for restraint: for subclinical hypothyroidism with a low TSH, randomized trials show no clear benefit of levothyroxine, and for positive antibodies with a normal thyroid the TABLET and T4LIFE trials showed no benefit. Testing has a place when there are symptoms — and not every value needs treatment.
⚕ Medically reviewed by Prof. Stratis Kolibianakis · Thessaloniki Medical Association Reg. No. 16340
ARTICLE 20 · FEMALE CONDITIONS & FERTILITY
