Some months you feel sharp and energetic in week two, and in the week before your period as though a different person has stepped in. That is not your imagination: four hormones rise and fall in a fixed rhythm, and that rhythm steers your energy, your mood and your fertility.
When I explain the cycle to women, the same penny drops every time: your hormones are not erratic, they follow a pattern. And once you know that pattern, you also understand why a hormone value only means something if you know which day the blood was drawn.
Below you walk through the four lead players, what they do per phase, and when to test each one.
The four hormones that steer your cycle
Oestrogen (oestradiol) builds up the uterine lining and lets a follicle mature. It rises in the first half of your cycle and peaks just before ovulation.
Progesterone takes over after ovulation and prepares the lining for a possible implantation. It is highest in the second half of your cycle and falls again if no pregnancy follows, which brings on your period.
FSH (follicle-stimulating hormone) puts the ovaries to work at the start of your cycle: it lets follicles grow.
LH (luteinising hormone) gives a sharp peak mid-cycle that triggers ovulation. Ovulation tests measure exactly this peak in your urine.
Which hormone do you test on which day?
This is where it often goes wrong: a fine progesterone value on day 3 means nothing, because progesterone is supposed to be low then. Each hormone has its own ideal moment. Cycle day 1 is the first day of real bleeding.
| Hormone | Best test moment | What the value shows |
|---|---|---|
| FSH | Cycle day 2 to 5 | How your ovaries respond to the start signal |
| LH | Cycle day 2 to 5 (baseline) or around ovulation | Ratio with FSH; the peak confirms ovulation |
| Oestradiol | Cycle day 2 to 5 | Baseline level of your oestrogen production |
| Progesterone | About 7 days before your expected period | Whether you actually ovulated |
With a 28-day cycle the progesterone measurement falls around day 21. Do you have a longer or shorter cycle? Then count back from your expected period, not from day 21.
What happens per phase?
The follicular phase (from day 1)
Your cycle starts on the first day of your period. FSH rises and lets a group of follicles grow, of which usually one takes the lead. That maturing follicle makes more and more oestrogen, which slowly builds up the uterine lining. Many women feel more energetic in this phase.
Ovulation (around the middle)
When oestrogen is high enough, your brain gives the signal for an LH peak. That peak makes the dominant follicle release the egg within about a day. This is your most fertile moment. According to NVOG, the professional body of gynaecologists, in a regular cycle ovulation takes place roughly two weeks before your next period, regardless of exactly how long your cycle is.
The luteal phase (until your next period)
The empty follicle turns into the corpus luteum and starts making progesterone. That keeps the lining in place. If no pregnancy follows, the corpus luteum dissolves, progesterone falls and your period begins. That fall can give complaints you may recognise as PMS.
What does this mean for your blood values?
A hormone value is never good or bad on its own: it either fits the phase you are in or it does not. A low progesterone value in the follicular phase is completely normal, while the same value a week before your period can point to a missed ovulation. If you want to check whether you ovulated, you look at progesterone in the second half of your cycle.
If you want the full picture, the Hormones Women panel brings together the hormones that steer your cycle in a single measurement. Every result is assessed by a BIG-registered doctor, so you are not left with loose numbers on your own.
Want to know which test suits which question? Then read our pillar on hormone testing in women.
Frequently asked questions
On which day do I test my hormones?
That depends on the hormone. FSH, LH and oestradiol are best measured early in your cycle (day 2 to 5), and progesterone about a week before your expected period. If in doubt, discuss with a doctor which moment suits your question.
Do I need to fast for a hormone test?
For the sex hormones, fasting is not needed. The timing in your cycle matters far more than whether you have eaten.
Can I track my cycle without a blood test?
Yes. An ovulation test measures the LH peak in your urine and your basal body temperature rises slightly after ovulation. A blood test additionally gives the absolute values, which can be useful if you have complaints or a wish to conceive.
References
- NVOG. Patient information on the menstrual cycle and fertility. Dutch Society for Obstetrics and Gynaecology. Available via nvog.nl.
- Thuisarts.nl. I want to understand how my period works. Dutch College of General Practitioners. Available via thuisarts.nl.
- NHG. NHG-Standaard Subfertiliteit. Dutch College of General Practitioners. Available via richtlijnen.nhg.org.
Every blood test result through Lunara includes a professional assessment by a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
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