Fertility investigation is the process of trying to identify whether there is a measurable reason why conception has not occurred — and if so, what it is. For women, this typically involves a combination of blood tests and imaging. This guide explains each test in the standard investigation panel, what it measures, how to get it, and how to interpret results.

When to Start Investigating

General guidance:

  • Under 35: Seek investigation after 12 months of trying without success
  • 35 or over: After 6 months of trying
  • Any age: Sooner if there is a known history of irregular periods, pelvic inflammatory disease, endometriosis, prior ectopic pregnancy, or known male factor

You can request a fertility investigation referral from your GP. Some tests — including AMH — are also available privately without a GP referral.

Blood Tests

AMH (Anti-Müllerian Hormone)

What it measures: The size of your remaining egg supply (ovarian reserve). AMH is produced by small antral follicles and reflects how many resting follicles remain in the ovaries.

When it's done: Any time of the menstrual cycle — AMH is stable across the cycle.

Normal ranges: Vary by lab, but broadly: above 10 pmol/L is normal for most reproductive-age women; 5–10 pmol/L is low-normal; below 5 pmol/L is low.

What it does NOT tell you: Egg quality. AMH predicts how many eggs are available, not whether they are chromosomally normal. A low AMH in a 32-year-old may not prevent pregnancy; a normal AMH in a 42-year-old does not guarantee chromosomally normal eggs.

Where to get it: Via GP referral (some GP practices will test; others refer to a fertility clinic or hospital for this). Privately, AMH tests are available from many fertility clinics and online testing services for approximately £50–£100.

For detail on AMH interpretation and NHS IVF eligibility, see AMH and IVF eligibility.

FSH and LH (Day 2–3 of Cycle)

What they measure: FSH (follicle-stimulating hormone) and LH (luteinising hormone) are the pituitary signals that drive follicle development. Day 2–3 baseline levels reflect how hard the pituitary is working to stimulate the ovaries.

  • High FSH (typically above 10 IU/L) suggests the pituitary is working harder, compensating for diminished ovarian response — consistent with reduced reserve
  • FSH is an older test that has been largely superseded by AMH as the primary reserve marker, but is still used alongside it
  • LH is relevant for assessing ovulation and — when elevated relative to FSH — for PCOS diagnosis

When it's done: Must be timed to Day 2–3 of the menstrual cycle (the early follicular phase).

Oestradiol (Day 2–3)

Often measured alongside FSH. A high baseline oestradiol (above approximately 200 pmol/L) can suppress FSH, making a "normal" FSH appear falsely reassuring — it may actually reflect poor reserve that is not being fully revealed by FSH alone.

Mid-Luteal Progesterone (Day 21, or 7 Days Before Expected Period)

What it measures: Confirms that ovulation has occurred. A progesterone level above approximately 30 nmol/L on Day 21 (or 7 days before the next expected period) confirms a likely ovulatory cycle.

When it's done: Day 21 of a 28-day cycle, or 7 days before the next expected period for irregular cycles. Timing is important — sampling too early or too late will miss the luteal peak.

Thyroid Function (TSH)

Thyroid dysfunction — both over- and under-active thyroid — can impair fertility and increase miscarriage risk. Subclinical hypothyroidism (TSH above the normal reference range, even without obvious symptoms) is associated with reduced conception rates and higher early pregnancy loss. NICE recommends thyroid testing as part of the fertility investigation panel.

Prolactin

Elevated prolactin (hyperprolactinaemia) can suppress ovulation. It is associated with galactorrhoea (unexplained nipple discharge) and irregular periods. If prolactin is elevated, investigation for a pituitary adenoma is appropriate before fertility treatment.

Rubella Immunity

Confirmed rubella immunity (or vaccination) is required before fertility treatment, as rubella in early pregnancy causes serious fetal abnormalities. If not immune, vaccination is offered before IVF begins (and you should avoid pregnancy for one month after the vaccine).

Ultrasound: Antral Follicle Count (AFC)

What it measures: The number of small resting follicles visible in both ovaries on transvaginal ultrasound. AFC is a direct ovarian reserve assessment and complements AMH — they measure related but not identical aspects of the follicle pool.

What a normal AFC looks like: Typically 8–15 follicles across both ovaries is considered normal for reproductive-age women. Higher counts (above 25) may suggest PCOS; lower counts (below 5) suggest diminished reserve.

When it's done: In the early follicular phase (Day 2–5 of cycle is ideal). It's a brief procedure — typically 5–10 minutes.

Availability: Via GP referral to a fertility clinic or gynaecology unit. Privately available at fertility clinics.

Tubal Patency Testing

Whether the fallopian tubes are open (patent) is one of the most important questions in the fertility investigation, as blocked tubes prevent natural conception.

Hysterosalpingography (HSG)

A contrast dye is injected through the cervix into the uterine cavity and fallopian tubes, and X-ray images are taken to confirm that the dye flows freely through both tubes. HSG is done under minimal or no anaesthetic and typically takes 15–30 minutes. Most patients experience cramping similar to period pain.

Performed as a day case at a hospital radiology department or fertility unit. Some evidence suggests a small fertility benefit from the procedure itself (flushing the tubes may temporarily improve fertility outcomes).

HyCoSy (Hysterosalpingo-Contrast-Sonography)

An ultrasound alternative to HSG in which contrast is passed through the tubes under transvaginal ultrasound guidance rather than X-ray. Does not involve radiation. Increasingly used in preference to HSG at many UK units.

Laparoscopy

Direct surgical inspection of the pelvic cavity, done under general anaesthetic. More invasive than HSG or HyCoSy, but allows direct visualisation of any endometriosis, adhesions, or peritubal disease that imaging cannot detect. Not done routinely as a first-line investigation — usually reserved for patients with symptoms suggestive of endometriosis or where imaging results are inconclusive.

Uterine Cavity Assessment

Saline infusion sonogram (SIS) / Sonohysterogram: Saline is introduced into the uterine cavity via a thin catheter while a transvaginal ultrasound is performed. This outlines the inside of the cavity and can identify polyps, fibroids within the cavity (submucosal), or adhesions.

Hysteroscopy: Direct visualisation of the uterine cavity using a thin camera inserted through the cervix. The definitive assessment of the uterine cavity — more informative than ultrasound for smaller polyps and adhesions. Can be done under local anaesthetic (outpatient) or light general anaesthetic.

Frequently Asked Questions

Q: Can I get fertility tests done on the NHS before I've been trying for a year?

A: Some GPs will arrange initial tests (particularly for patients with irregular periods or known risk factors) even before the 12-month mark. AMH in particular may be available if there are clinical reasons. If your GP is unwilling and you don't want to wait, private AMH and AFC testing is available from fertility clinics and online services.

Q: My AMH is normal but my FSH is high. Which result should I trust?

A: Both provide useful information. High FSH with normal AMH can occur but is unusual — confirm the FSH timing (it must be Day 2–3). It's worth repeating both tests in a subsequent cycle. Your fertility specialist should interpret the full picture rather than either marker in isolation.

Q: My tubes are open on HSG but I still can't conceive. Why?

A: Patent tubes are necessary but not sufficient for natural conception. Many factors — egg quality, sperm function, timing of ovulation, endometrial receptivity — affect conception independently of tubal patency. Normal tubal patency rules out one cause; it doesn't guarantee conception.

Q: I've been told I have polycystic ovaries on ultrasound. Does that mean I have PCOS?

A: Not necessarily. Polycystic ovary morphology (many small follicles on ultrasound) is one feature of PCOS, but a PCOS diagnosis requires two of three criteria under the Rotterdam criteria: polycystic ovary morphology, irregular or absent ovulation, or clinical/biochemical signs of excess androgens. Discuss the full diagnostic picture with your GP or gynaecologist.

Q: Do I need all these tests before seeing a fertility specialist?

A: Some tests are routinely done by GPs before referral (AMH, Day 21 progesterone, semen analysis for a partner). Others are done at the fertility clinic. It is worth asking your GP which tests they can arrange before your first clinic appointment — arriving with complete results avoids a waiting cycle at the clinic for investigations.

This article is for information only and does not constitute medical advice. Test result interpretation should always be done by a qualified clinician in the context of your full history.