How it All Works

While estrogen and testosterone levels slide steadily downward from twenty-six years of age on, when human growth hormone slows, the biggest difference between a woman in her twenties and a woman in her late thirties is in the levels of progesterone she can produce.

In a normal twenty-year old, the act of ovulating -- which produces progesterone, once a month for fourteen days -- is dependent on a system of feedback loops between the ovaries and the brain which are regulated by levels of estrogen. Estrogen production is directly dependent upon the number of eggs a woman has left every month after ovulation, deducted from the finite number we are born with.

Ovulation uses up about 150 every month in an effort to produce one “good” one. From conception until puberty, eggs are destroyed by a genetic clock. As fetuses, in utero, we had about one million eggs, but by the time we were born -- we were down to half a million. At puberty we’re down again by half, to a quarter of a million. Every seven years after puberty the number of eggs diminishes by one half of the declining baseuntil we reach about thirty-three, when the decline picks-up speed, and the number of eggs are halved every three years.

In the ten to fifteen years before we actually hit the wall sometime in our fifties, and run out of eggs, the declining estrogen falls in step-fashion with the declining egg base. Therefore, ovulating the remaining eggs gets “iffier” as time goes by (since the system is run by estrogen) and fertility is truly at risk by the time we are in our midthirties; because we don’t have enough estrogen to tell the brain to send the signal to ovulate, at least not on a regular basis.

So, as we’re running out of eggs, the estrogen signal from our ovaries to our brain is weak. The weak estrogen signal is ultimately responsible for the loss of progesterone since progesterone seeps from the blister that housed the egg. -- No pop, no progesterone. The first hint of estrogen depletion is shorter or longer menstrual periods as I mentioned before. The other earliest symptoms are sleeplessness, inability to concentrate or “mind noise,” loss of libido and weight gain. And let us not forget the wrinkles.

In peri-menopause (age thirty-three to fifty), internal estrogen levels certainly aren’t high enough anymore to reliably ovulate, but they are just high enough for too long to be “normal.” Normal levels of progesterone would bring it down. But we don’t have normal levels anymore. It’s like a game of dominoes.
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