This is how it works: over the course of 10-14 days the egg will grow from immaturity within an antral follicle, and turn into a large, hopefully-soon-to-be-fertilized, mature egg in its dominant follicle. Both the egg and the follicle have to be functioning properly for the cycle to go well.

The dominant follicle makes estrogen, and once you ovulate, progesterone. Estrogen and progesterone together govern the activity of your uterus, which you experience as your menstrual cycle.

If you have a healthy egg, you have a healthy follicle and you expect a healthy menstrual cycle. This means the reverse is true too: when we think that your menstrual cycle is going well, we strongly suspect that you must be making healthy, high quality eggs.

Here are the factors that we look at when deciding if a given menstrual cycle is going well:

Menstrual Cycle History

Day of ovulation

Ideally ovulation will occur on days 11 or 12. Delayed ovulation – day 13 or later – is not a sign of egg quality concerns; in fact, it is more commonly a sign of an excess ovarian reserve, which is generally a good thing. But early ovulation – days 8,9, or 10 of the cycle – implies lower quality eggs.

Premenstrual Spotting

Once the egg is released, the leftover follicle (now called a corpus luteal cyst) makes progesterone. Progesterone stabilizes the lining of the uterus. A low-quality follicle is less likely to be associated with enough progesterone, and therefore the woman may notice a shorter luteal phase and/or premenstrual spotting.

Cycle Length

Long cycles are ok, but short cycles are not. If previously-28-day-cycles are now 26 days, it suggests egg quality is failing. Cycles are shorter because of the early ovulation and shortened luteal phases described above.

Menstrual Cycle Lab Values

Peak Estrogen

When a woman is about to ovulate, estrogen will be at its maximum level. Estrogen effects may be noticed as spinnbarkeit. We can also measure estrogen levels through blood tests; peak estradiol is between 500 and 1000 pmol/litre per healthy follicle. When cycle monitoring, ask your clinical team what your peak estrogen was: bigger numbers are better. If the level is towards 500 (or lower) per mature follicle, then egg quality may be a concern.

Peak Progesterone

Progesterone is made by a healthy corpus luteal cyst. Peak progesterone values, traditionally measured on “day 21″ of your cycle (but more accurately recorded 7 days after ovulation) is usually 30 ng/ml or higher for a fertile cycle.

I can write to all this in greater detail if you are interested; the relationships between eggs, follicles, hormones, and the menstrual cycle is complicated but fascinating. (Well, fascinating if you are a Reproductive Endocrinologist…)

But the important part is, because of these inter-relationships, we can help you to maximize the likelihood of releasing a good egg in the next cycle by manipulating hormones in this cycle. It is called estrogen priming, and will be the subject of another post.

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