Aging and Female Fertility Potential

Of the three most common factors playing a role in human fertility (egg quality, sperm quality, and the function of Fallopian tubes), egg quality is the most important for the probability of a successful pregnancy.

The quality of eggs within the ovaries, rather than the receptivity of the uterus, determines female fertility potential. At Bay IVF, we use the Ovarian Reserve Assay (ORA) together with the reproductive history and an ultrasound examination of the ovaries to assess the female fertility potential.

At birth, a newborn girl has approximately two million eggs within her ovaries. By the time she starts ovulating, she has about 400,000 eggs remaining. From that point on, the ovaries lose approximately 30 eggs a day. During her reproductive years, a woman ovulates approximately 400 eggs.

Female fertility begins to decline many years before menopause despite continued regular ovulations. The likelihood of a successful pregnancy decreases by approximately 10% to 15% each year after the age of 30 to 33 and at an even faster rate after the age of 40.

The following graph illustrates the impact of female age on the female fertility potential:

 

The decrease in female fertility potential is due to the loss of high-quality eggs. This age-related loss of fertility magnifies the impact of any other infertility factor present.

As a woman ages, the remaining eggs in her ovaries also age, rendering them less capable of fertilization and of being able to develop into healthy embryos. In addition, fertilization of these eggs, whether spontaneous or in a laboratory, is associated with a higher risk of miscarriages and genetic disorders. The vast majority of genetically abnormal pregnancies end very early, often resembling a normal menstrual period.

The risk of chromosomal abnormality in newborns by maternal age:

Risk of Chromosomal Abnormalities

Maternal Age	Chromosomal Abnormalities
20	1/526
25	1/476
30	1/385
35	1/192
40	1/66
41	1/53
42	1/42
43	1/33
44	1/26
45	1/21

 

The likelihood of a fertilized egg implanting is related to the age of the woman who produced the egg and not to the receptivity of the uterus (which does not decrease with age). For example, in the Donor Egg IVF treatment, egg donors are typically young women in their twenties, thus the success rate for the Donor Egg IVF treatment varies only slightly regardless of the age of the embryo recipient.

The following illustrations, from the Centers for Disease Control (CDC) compilation of national In Vitro Fertilization and Donor Egg IVF data, show the impact of female age on the female fertility potential.

Many infertility specialists recommend that women over the age of 37 years, who are trying to conceive, should proceed to In Vitro Fertilization quickly before their remaining fertility potential is lost.

 

The risk for miscarriage increases among women in their mid-to-late thirties and continues to grow with age, reaching over 40% by the age of 42 years. The miscarriage rates observed among women undergoing advanced reproductive treatments appear to be no higher than in pregnancies conceived through intercourse.