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Ovarian Reserve And Fertility

What’s age got to do with fertility?

oocyte human eggOvarian Reserve and Fertility — the number and quality of eggs a woman has available when she tries to become pregnant—is the major factor that links age and infertility. (Human oocyte "egg" pictured at right).

Female fertility is fixed very early in life. Primordial cells that will become eggs (oocytes) begin to develop in the human fetus by the 7th week of gestation, and the total number peaks at 20 weeks gestation. From a peak of 6 to 7 million, the oocyte number declines to about 350,000 by birth. By puberty, 200,000 follicles on average (fluid filled sacs in the ovary that contain oocytes) remain in a woman’s ovaries.

From puberty to menopause, 99.9% of oocytes are lost due to the monthly process of the reproductive organs, which includes the selection of one oocyte for possible fertilization while others that have developed during that month are victims of apoptosis (programmed cell death). This decades-long process is, in fact, the body’s natural progression to eventual ovarian failure and infertility.

So, excluding any other factors that might prevent pregnancy, age and the decline of ovarian reserve has a lot to do with infertility. The statistics reported by the Centers for Disease Control and Prevention indicate that the following percentage of women who are infertile by age group:

  • 7% by age 30
  • 11% by age 34
  • 33% from age 35 to age 40
  • 87% by age 45