Hormones & blood testsDraft: awaiting clinical review

Progesterone

Produced after ovulation; a blood test about a week before your period can confirm that ovulation has happened.

Overview

After ovulation, the follicle that released the egg becomes the corpus luteum, which produces progesterone. This prepares the womb lining for implantation.

A 'day 21 progesterone' test is only correctly timed in a 28-day cycle. The test should be done about 7 days before the next expected period.

What is well established

A mid-luteal progesterone level is a standard way to confirm ovulation in people with regular cycles.
With irregular cycles, the test may need to be done later and repeated until the next period starts.
For people with bleeding in early pregnancy who have had a previous miscarriage, NICE recommends offering vaginal micronised progesterone.

Uncertain or emerging evidence

Low progesterone in the second half of the cycle ('luteal phase deficiency') has not been established as an independent cause of infertility, and routine progesterone supplementation outside specific situations is not supported by strong evidence.

This guide is general information and does not replace advice about your own circumstances. Clinical review pending.