Female hormones shift dramatically across the menstrual cycle. The right day for testing is the difference between a useful result and an uninterpretable one.
Day 3 of cycle
FSH, LH and oestradiol are tested on day 3 (counting from the first day of your period). This is the early follicular phase and gives the cleanest baseline. Day 1 to 5 is generally acceptable; day 3 is the convention.
Day 21 of cycle (or 7 days before next period)
Progesterone is tested 7 days after ovulation. In a 28-day cycle that is day 21. In a 30-day cycle it is day 23. The point is 7 days before the next expected period. A progesterone above 30 nmol/L confirms ovulation occurred.
Any day of cycle
AMH (ovarian reserve), thyroid markers (TSH, free T4, free T3), prolactin, sex hormone binding globulin and testosterone can all be tested on any day of the cycle. Hormonal contraception affects the readings, see below.
Hormonal contraception
If you are on hormonal contraception, hormone readings will reflect synthetic hormones rather than your natural baseline. For a true baseline, allow 2 to 3 months after stopping before testing. Use an alternative form of contraception in the meantime. Chxhealth is a biomarker and genetic data provider. We do not diagnose, treat or prescribe. Our service supports your wellbeing journey alongside your healthcare professional.
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Frequently asked questions
What if my cycle is irregular?
AMH and most markers can be tested any day. For FSH and oestradiol baseline, the convention is days 1 to 5 if cycling, or any day if cycles have stopped.
What if I miss day 21 for progesterone?
Test 7 days before your expected next period. Day 21 is only correct for a 28-day cycle.
About this article. Educational content. Chxhealth is a biomarker and genetic data provider. We do not diagnose, treat or prescribe. Our service supports your wellbeing journey alongside your healthcare professional. For medical advice about your health or results, please speak to a qualified clinician.
