A woman plays many important roles throughout her lifetime, and reproduction often remains an important one as menopause approaches. Some women are scrambling to have a child, others are hoping not to. In either case, perimenopause is a time that fertility ebbs and wanes and as a result, estrogen levels fluctuate with it.
Today, reproduction and menopause are merging closer and closer because women often delay having children – trying to start their careers before their families, or waiting later to marry, or entering a second marriage are just some of the reasons. In 1990, only 9% of women were having their first child after the age of 35; today, one in 5 women in the United States has her first child after age 35. About one-third of women where the woman is over 35 have fertility problems.
The decline in fertility and its accompanying fluctuating estrogen levels are what cause most of the symptoms of perimenopause. Hormonally, the body works like a thermostat. The pituitary gland located at the base of the brain produces a hormone called follicle-stimulating hormone (FSH) because it stimulates the growth and development of follicles, which includes an egg and the fluid filled sac surrounding it. Human eggs are actually produced while a female baby is still in her mother’s uterus. During the middle months of pregnancy, the numbers of eggs rise to about 7 million. In this time of rapid egg production, the developing female baby produces high levels of FSH. Over the last half of pregnancy, the numbers of eggs rise to about 7 million. In this time of rapid egg production, the developing female baby produces high levels of FSH. Over the last half of pregnancy, FSH levels drop sharply and so do the number of eggs. By birth the number is reduced to 400,000. (Bar-Ami S, Seibel MM. Oocyte development and meiosis in humans. In. Seibel MM. Infertility: A Comprehensive Text. Appleton & Lange. Norwalk, Ct. 1997.)
These eggs lie dormant within the ovaries until puberty when very low FSH levels rise slightly to the normal adult range and each month signal a group of 10 to 20 eggs to mature. The cells around these eggs start producing estrogen, which signals the pituitary gland to stop making more FSH. The estrogen also thickens and prepares the uterine lining in case there is a pregnancy. After a week or so, one of the eggs in the group is selected as the dominant one for that month’s group and a week later it is released – a process called ovulation. After releasing the egg, the follicle becomes a corpus luteum and its cells begin to produce progesterone as well as estrogen. The progesterone stabilizes the uterine lining and prepares it to receive a fertilized egg. If a fertilized egg doesn’t implant and cause a pregnancy, estrogen and progesterone levels drop at the end of two weeks, the old lining is shed as a menstrual period, and the whole process repeats.
Fertility begins to decline after age 35. But around age 38 eggs are lost from the ovaries at an even faster rate, and the symptoms of perimenopause often get started about that time. By best estimates, at age 40 a woman has 5,000 to 10 thousand eggs left. Those remaining eggs often respond less well to FSH and may not ovulate. I usually explain to patients that the FSH “asks” the ovaries to make an egg develop, but because the ovaries “don’t hear it as well,” the pituitary gland speaks “louder.” Of course the real reason is that the less responsive cells around the eggs produce less estrogen (and less of another hormone called inhibin whose job it is to keep FSH levels lower), allowing FSH levels to rise. Another hormone called anti-mullerian hormone or AMH is another indication of fertility. I talked about it in the earlier video. AMH levels in the most fertile range of reproduction are above 1 ng/ml (nanograms per milliliter). Levels that suggest low fertility and somewhere close to menopause are approximately 0.3 to 0.6 ng/ml or less.
Most women who conceive easily have fertile levels of AMH, FSH levels of 10 mIU/ml (the units stand for milli-international units per milliliter) or less. FSH levels above 15 mIU/ml suggest perimenopause is at hand, and levels above 30 to 40 mIU/ml help to confirm menopause has arrived. But FSH levels do fluctuate from month-to-month, especially in perimenopause so no one value is foolproof. If you are taking a birth control pill or other estrogen or progesterone medication, they will artificially lower FSH levels. That’s why you have to stop taking them for a week or so to get an accurate FSH measurement.
Of course, if you are in perimenopause and need a contraceptive, keep using one that is non-hormonal (such as a condom or diaphragm) while you wait to check your FSH level.
Until next time,
Dr. Mache Seibel, Founder of My Menopause Magazine http://bit.ly/MyMenoMag
Professor, University of Massachusetts Medical School
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