Fertility Blood Tests for Women: FSH, LH, AMH & Progesterone

When Are Fertility Blood Tests Recommended?

NICE guidelines (CG156) recommend that couples who have not conceived after 12 months of regular, unprotected intercourse should be offered initial fertility investigations. For women aged 36 or over, investigations may be started after 6 months. Fertility blood tests are a central part of these investigations, helping to assess ovarian function, hormone balance, and whether ovulation is occurring.

Many women also choose to have fertility blood tests proactively — for example, before starting IVF, after stopping contraception, or simply to understand their reproductive health and ovarian reserve.

AMH (Anti-Müllerian Hormone)

AMH is produced by the small follicles in the ovaries and is the most reliable marker of ovarian reserve — effectively, the number of eggs you have remaining. Unlike other fertility hormones, AMH is relatively stable throughout the menstrual cycle, so it can be tested on any day.

• High AMH (above 25 pmol/L) — Suggests a high ovarian reserve. Very high levels may indicate polycystic ovary syndrome (PCOS).
• Normal AMH (approximately 7 to 25 pmol/L) — Reassuring ovarian reserve for age.
• Low AMH (below 7 pmol/L) — Suggests a diminished ovarian reserve. This does not mean you cannot conceive naturally, but it may influence decisions about the timing of treatment.

AMH naturally declines with age. A woman of 25 will typically have a higher AMH than a woman of 38, even if both are fertile. The test is most useful when interpreted alongside your age and other hormone results.

FSH (Follicle-Stimulating Hormone)

FSH is produced by the pituitary gland and stimulates the ovaries to develop follicles (each containing an egg). It should be tested on day 2, 3, 4, or 5 of your menstrual cycle (day 1 is the first day of your period).

• Normal early-follicular FSH — Approximately 3.5 to 12.5 IU/L.
• Raised FSH (above 10 to 12 IU/L in the early follicular phase) — Suggests the pituitary is working harder to stimulate the ovaries, which may indicate a declining ovarian reserve.
• Very high FSH (above 25 IU/L) — May indicate premature ovarian insufficiency or approaching menopause.

LH (Luteinising Hormone)

LH works alongside FSH to regulate the menstrual cycle. A surge in LH mid-cycle triggers ovulation. LH should be tested at the same time as FSH (day 2 to 5).

• Normal early-follicular LH — Approximately 2.4 to 12.6 IU/L.
• LH:FSH ratio — In PCOS, LH is often elevated relative to FSH, with a ratio of 2:1 or higher. This is suggestive but not diagnostic on its own.

Oestradiol (Estradiol / E2)

Oestradiol is the main form of oestrogen produced by the ovaries. It is typically tested alongside FSH on day 2 to 5. In the early follicular phase, oestradiol should be relatively low (approximately 100 to 400 pmol/L). A high early-follicular oestradiol can suppress FSH, potentially masking a true elevation and giving a falsely reassuring FSH result.

Progesterone (Day 21 Test)

Progesterone is produced by the corpus luteum after ovulation. A "day 21 progesterone" test is used to confirm whether ovulation has occurred. Strictly, it should be taken 7 days before your expected period — so if your cycle is 35 days, test on day 28; if your cycle is 28 days, test on day 21.

• Above 30 nmol/L — Confirms that ovulation has occurred.
• 16 to 30 nmol/L — Borderline — may indicate ovulation or a suboptimal luteal phase. Repeat testing may be advised.
• Below 16 nmol/L — Suggests ovulation has not occurred in that cycle.

If progesterone is low, your GP may repeat the test in a subsequent cycle before concluding that you are not ovulating, as occasional anovulatory cycles are normal.

Prolactin

Prolactin is a hormone produced by the pituitary gland. High levels of prolactin (hyperprolactinaemia) can suppress ovulation and cause irregular or absent periods. Common causes of raised prolactin include stress, certain medications (including antipsychotics and anti-sickness drugs), and, rarely, a pituitary adenoma.

Normal prolactin is approximately 100 to 500 mU/L. It is best measured in a relaxed state, ideally mid-morning and at least an hour after waking.

Thyroid Function

Thyroid disorders can significantly affect fertility and early pregnancy. Both hypothyroidism and hyperthyroidism can cause irregular periods, anovulation, and increased risk of miscarriage. TSH should be checked as part of any fertility investigation. For more detail, see our guide on thyroid blood tests.

Age-Related Changes

Female fertility declines with age, and this is reflected in hormone levels. AMH falls progressively, while FSH tends to rise as the pituitary works harder to stimulate ageing ovaries. The decline accelerates after age 35 and becomes more pronounced after 40. Understanding your current hormone profile can help you and your doctor make informed decisions about the timing of treatment.

Getting Tested at Home

Timing is important for fertility blood tests — many need to be done on specific days of your cycle. A home phlebotomy appointment through Lola Dispatch can be booked for the exact day you need, at a time that suits you. This is far more convenient than trying to secure a GP appointment on the right cycle day.

All Lola Dispatch phlebotomists are DBS-checked and qualified. Book a home blood test to take the stress out of fertility testing and get your results within 24 to 48 hours.