What Blood Tests Are Done for Fertility?

When you're trying to conceive, blood tests can't guarantee a pregnancy — but they can build a helpful picture of your hormones, whether you're ovulating, and whether anything treatable is getting in the way. They're usually one of the first steps a clinician suggests, alongside looking at both partners. Here's what the common fertility blood tests actually measure.

The hormones that shape your cycle

A handful of hormones work together to release an egg each month. Testing them helps show whether that process is running smoothly:

• FSH (follicle-stimulating hormone) — helps eggs mature; an early-cycle level gives a rough sense of ovarian activity.
• LH (luteinising hormone) — surges to trigger ovulation.
• Oestradiol — the main form of oestrogen, which rises as an egg develops.
• Progesterone — rises after ovulation, so a mid-luteal level is the classic way to confirm that ovulation has happened.
• Prolactin — a raised level can interfere with ovulation and periods.
• Testosterone and SHBG — raised androgens can point towards PCOS, a common cause of irregular cycles.

Thyroid and general health

Your thyroid has a strong influence on fertility, so thyroid function (TSH and free T4) is usually checked too — both an underactive and an overactive thyroid can disrupt cycles and affect early pregnancy. Broader checks such as blood count and vitamin levels are also sometimes included when planning a pregnancy.

AMH — your ovarian reserve

Anti-Müllerian hormone (AMH) reflects the number of eggs remaining in the ovaries. It's widely used in fertility planning and before treatments like IVF. Importantly, AMH indicates quantity, not quality — a lower level doesn't mean you can't conceive naturally, and a good level isn't a guarantee. It's best interpreted alongside your age and the rest of your results.

Timing matters

Because these hormones change across your cycle, timing affects what the numbers mean. FSH, LH and oestradiol are typically measured on days 2–5 of your period, while progesterone is checked around day 21 (about 7 days before your next period is due) to confirm ovulation. AMH and prolactin can be taken at any point. If your periods are irregular or absent, our team can advise on the best approach.

Fertility involves both partners

Around half of fertility difficulties involve a factor on the male side, so a full assessment usually looks at both partners — often including a semen analysis for the male partner. Blood tests are one piece of the picture, not the whole of it.

When to get checked

General guidance is to seek advice after 12 months of trying (or 6 months if you're over 35, or sooner if your periods are irregular or you have a known gynaecological condition). Testing early can be reassuring and, where something needs attention, gives you a head start on a plan with your doctor.

Written by Dr Ibrar Ahmed — MBChB MRCP MRCGP PhD PG Dip (Cardiology)
Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic