Hormones rise and fall through the menstrual cycle. Test them on the wrong day and you'll get a perfectly accurate number that's practically meaningless. Here's the simple rulebook we use at Her Form.
Day 3 (early follicular)
Day 3 is the reference baseline — best for ovarian reserve and the early-cycle hormone pattern.
- •FSH, LH and the ratio between them
- •Estradiol (baseline)
- •AMH (technically any day — stable across the cycle)
Day 21 (mid-luteal)
The luteal phase exists only after ovulation — these markers are useless any other time.
- •Progesterone (confirms ovulation)
- •Estradiol (peak luteal — the estradiol:progesterone ratio)
Any day
These are stable enough across the cycle to test whenever:
- •TSH, free T4, free T3, TPO antibodies
- •AMH
- •Fasting insulin, HbA1c
- •Vitamin D, B12, ferritin
- •Total and free testosterone, SHBG, DHEA-S
- •Cortisol (AM only)
Irregular cycles, no cycles, or on the pill
If cycles are irregular, we usually test the cycle-independent markers first and time a second luteal draw if needed. On the pill, sex hormones are suppressed and don't reflect your baseline — we test off the pill (ideally 3 months) for an accurate picture.
Frequently asked
Day 19–22 of a 28-day cycle is fine. The key is being roughly 7 days after ovulation — we adjust for longer or shorter cycles.