Diminishing Fertility with Age

It seems that everyone has heard stories or knows of someone who has become pregnant after the age of 44.  However, pregnancies are actually fairly rare at that age.The oldest woman documented to give birth with the use of her own eggs is 54 years of age.Many scientific studies have shown that a woman’s fertility (the chance of conceiving in a given month) declines a small amount after the age of 34.The odds of conceiving decline even more rapidly after the age of 39.

For a woman wanting to delay child-bearing, it must seem unfair that her fertility declines with age sooner and more substantially than a man’s fertility.Why the difference between the sexes?The biological answer is that men continue to make new sperm cells every day of their adult lives.Women, on the other hand, are born with all of the eggs they will ever have.New ones cannot be made. Thus a 40 year old woman has eggs that have been around for 40 years.They’ve been exposed to various toxins and cosmic radiation over the years.

Contrast this to a man’s sperm which is only a few days or weeks old.In addition to the problem with aging eggs, a woman has to contend with the fact that her supply of eggs is limited and will eventually be exhausted.Menopause marks the time when no more usable eggs remain.The average age of menopause is 50.A woman has approximately 300,000 immature eggs in her body at the time of puberty.So what became of those eggs between puberty and menopause?Were they all released during the once-a-month ovulation process?No.Usually only one egg will reach the fully mature state necessary to ovulate during each menstrual cycle.The average woman has 450 menstrual cycles during her lifetime.The other 299,550 or so eggs slowly degenerate over time at a rate of about 25 per day.Fertility medications will not alter this rate of egg degeneration.Some things are known to speed up the loss of eggs, such as chemotherapies or radiation treatments used to fight cancer.Smoking cigarettes or marijuana also appears to hasten the depletion of usable eggs.In fact, menopause typically arrives one or two years earlier in women who smoke.

A woman who has a diminished number of remaining eggs has a lower chance of conceiving a pregnancy with her own eggs, even using fertility treatments.This is true even when the woman is still having regular menstrual cycles.In these cases the eggs that remain are less likely to fertilize and the resulting embryo is less likely to continue to grow.Why?It is hypothesized that the “bottom of the barrel” eggs are less optimal because the best ones have already been selected earlier.

Many women have fears that their chances of having a baby with Down’s Syndrome or other chromosomal abnormalities is outrageously high.In fact at age 40, the chances of having a pregnancy with such an abnormality reach the 4th month of pregnancy is fairly low – only 3%.One risk, however, that is increased is the chance of miscarriage.On average 50% of the pregnancies in women over the age of 39 will spontaneously abort.The common reason for these miscarriages is a chromosomal imbalance that is not compatible with further fetal development.

Just because a woman is over 40 years of age doesn’t mean she needs to give up all hope of having a baby.There is a simple blood test that her gynecologist or fertility specialist can order to help determine if she has an adequate reserve of eggs to allow for a reasonable chance of becoming pregnant.This test checks the level of FSH and Estradiol.It must be obtained on the 2nd, 3rd or 4th day of the menstrual cycle.If possible, a woman who wishes to have a child should try to conceive before her mid 30’s.Sometimes a woman will begin running low on usable eggs even in her early 30’s.Fortunately there is one successful treatment for women who lack a sufficient egg reserve.The use of donated eggs allows these women to carry a pregnancy that is genetically related to her husband even though it is not her genetic offspring.Such a “donor egg cycle” uses the technique of IVF with the eggs of a willing donor.The oldest woman to deliver a baby through the donor egg technique was 67 years old! Obviously, not all women want to get pregnant after the age of 45.However for those who do, this technology allows those women to enjoy the same reproductive flexibility as men have had with regard to delaying family building.


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