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Aging and Fertility in Women

Aging and fertility in women are inversely related. As a women ages over 20 years of age, monthly fertility declines. Women are born with all the eggs they well ever have. Each month after puberty, typically one egg will ovulate whereas most eggs die off from atresia each month. Just as a young woman has more energy than an older woman, a younger egg has more energy and an older woman’s egg. Much energy is needed for the egg to complete fertilization and control the cross over of genetic material during meiosis. The egg’s energy is one of the many factors that dictates the embryo’s fate until the embryo can attach to the blood and glucose supply of the uterine lining.  

Recent interest in the reproductive capability of older women has been prompted by the unprecedented numbers of women presenting for fertility treatments after delaying childbearing into their late 30’s and 40’s. The impact of aging on fertility has become increasingly relevant as increased percentages of American women are having their first child after the age of 35, a 50% increase in the last 2 decades.

Demographic studies demonstrate a consistent decline in fecundity (monthly fertility rates) after age 30 to 35. It is twice as hard for a woman to conceive at age 35 as it is at age 25. In women over 40 years of age, involuntary infertility approaches 65% of women. If all fertility factors are perfect, at age 38, the best anticipated monthly fertility rate in a woman without infertility is 8%/month. At age 40, the best anticipated monthly fertility rate in women without infertility is 3-5%/month. It is much harder to get pregnant than people are aware of.  

As a woman ages, there are both decreased monthly fertility rates and an increased miscarriage rate. The dominant factor that causes age related reduced fertility is the decline in egg quality. This decline is marked by an acceleration in follicular atresia, and increased rate of chromosomal abnormalities in resultant embryos, and decreased ovarian reserve.   Follicle stimulating hormone (FSH), antimullarian hormone (AMH), and ovarian antral follicle counts (AFC) are surrogate markers of ovarian reserve. Age related increased miscarriage rates are largely due to increased number of genetic abnormalities in resultant embryos.

Both age and ovarian reserve make independent contributions when predicting response to fertility hormone stimulation. A woman of advanced reproductive age with a normal ovarian reserve marker still must contend with age related decline in fertility due to diminished egg quality. Because invitro fertilization (IVF) success rates are proportional to the number of eggs that are retrieved, fertilized, and transferred, age-related low responders with poor follicular development have diminished pregnancy rates.

Women aged 43 years and older often proceed directly to oocyte donation to increase their chances of having a healthy child. Oocyte donation has become a viable option for those women whose infertility is age-related. Oocytes collected from super ovulated egg donors are fertilized with sperm. The resulting embryos are then transferred to the recipient who has been treated with estrogen and progesterone to produce an endometrial environment suitable for implantation. Excellent success rates can be achieved through oocyte donation in women up to and beyond the age of 50 years.