Five hormones run the menstrual cycle: GnRH, FSH, estrogen, LH and progesterone. In precise sequence, they mature an egg, prepare it for fertilization and prepare the uterus for a possible pregnancy. If pregnancy doesn't happen, everything is shed and the process starts over.
Every menstrual cycle is a small choreographed miracle. The process lasts between 21 and 35 days, and each hormone has a precise part in it:
| Hormone | Produced by | Role in the cycle |
|---|---|---|
| GnRH | Hypothalamus | The conductor: tells the pituitary to release FSH and LH |
| FSH | Pituitary | Opens the competition: starts 5 to 20 follicles maturing |
| Estrogen (estradiol) | Dominant follicle | Growth hormone of the first half; its peak triggers ovulation |
| LH | Pituitary | The trigger: its surge leads to ovulation |
| Progesterone | Corpus luteum | Guardian of the second half: keeps the endometrium receptive |
Map to the Positive, Chapter 13.
Produced by the hypothalamus, it fires pulses every 60 to 90 minutes, telling the pituitary to release FSH and LH. Without a steady GnRH rhythm, the whole cycle falls apart. Chronic stress, extreme weight loss, excessive exercise and sleep disorders all directly affect these pulses.
At the start of each cycle, FSH stimulates between 5 and 20 follicles to begin maturing in the ovaries. As one follicle becomes dominant, FSH drops. High FSH on day 3 of the cycle is a sign of diminished ovarian reserve: the body has to “shout” louder to get a response from the ovaries.
Produced by the dominant follicle, estradiol does three essential things: it thickens the endometrium, it turns cervical mucus into a sperm-friendly medium and, when it hits a critical peak, it triggers ovulation.
When estradiol reaches about 200 pg/mL and holds that level for 50 hours, the pituitary releases a surge of LH. Ovulation occurs 24 to 36 hours after that surge. Ovulation tests detect exactly this LH surge.
Produced by the corpus luteum (the empty follicle after ovulation), it keeps the endometrium receptive, suppresses new ovulations and, if there is a pregnancy, sustains the first 10 days until the placenta takes over.
It's exactly the precision of this choreography that makes it fragile. One hormone out of place, one phase shorter than it should be, a weak ovarian response, and the whole cycle can look “normal” without being fertile.
These hormones leave traces you can read in your own body. Estrogen turns cervical mucus fertile. The LH surge is what an ovulation test detects. Progesterone raises your basal body temperature after ovulation.
The five hormones open Chapter 13 of Map to the Positive, the first chapter of Station II. The same chapter covers what defines a normal cycle and the short luteal phase, and the chapters that follow teach you to read these hormones at work in your own body: cervical mucus, basal temperature, ovulation tests and secondary signs.
Take 30 days. If it does not give you more clarity than everything you have read for free so far, ask for a refund and you get every cent back. We cannot promise you a pregnancy. We can promise you will not be guessing.
References: ASRM Practice Committee. Diagnostic evaluation of the infertile female, 2021.