The Impact of Age on Female Fertility
The attrition of egg loss from birth until menopause is truly staggering. By adolescence, 90% of the eggs available for ovulation are gone, leaving about 100,000 eggs remaining from the original 2 million at birth. The eggs are microscopic cells lying within protective capsules called follicles which are located in the ovaries.
Each egg is formed with a pre-determined lifespan that is as brief as a few days or up to many years. Unlike ongoing fresh sperm production in men, there is absolutely no new formation of fresh eggs in women. In fact it is estimated that only about 400 healthy eggs are released during a woman’s reproductive years.
What Happens to Reproduction as Women Age?
Human reproduction is rather inefficient. Even during the peak reproductive ages such as the teen years and the 20’s, the chance of pregnancy is roughly 20% per month. This is assuming that a woman has regular ovulation with open fallopian tubes and a partner with normal sperm production.
If any of these factors are disrupted, it can lead to infertility or it can prolong the time needed to become pregnant. Additional gynecologic problems such as endometriosis, pelvic scarring, and uterine fibroid tumors can interfere with the normal process of egg entry into the fallopian tubes or failed implantation of the embryo.
Chromosomal and Genetic Abnormalities Associated with Aging
The most common type of birth defects are associated with the formation of abnormal numbers of chromosomes in the embryo. Chromosomes are microscopic twigs of genetic information inside the egg nucleus which contain vital DNA information necessary for the development of a normal child.
During embryo development there must be an exact replication of chromosomes each time the embryonic cells divide. During egg division, if the fertilized egg fails to transfer the normal number of chromosomes to its daughter cells, the embryo will carry an abnormal number of chromosomes leading to defective embryos which can fail to implant or lead to a miscarriage.
Other chromosomal problems can occur when entire chromosomes can be lost, duplicated or become fragmented. Aneuplody is the name given to the conditions arising when abnormal embryos are carried by an embryo. The best known example of these types of chromosomal errors is Down Syndrome where one extra third chromosome develops in the 21st pair of chromosomes. This may lead to a birth defect or an early pregnancy loss.
What Happens to the Internal Structure of Aging Eggs?
The cellular fluid inside the egg contains many tiny organelles and the so called cytoskeleton. Spontaneous deterioration of the egg’s internal protein structures, like the mitochondria, will cause a disturbance in the normal steps of the fertilization process.
The meiotic spindle is a fragile and complex structure responsible for proper chromosome alignment and separation. When the spindle fails to perform correctly suboptimal embryos will develop, leading to implantation failure or miscarriage during the first few weeks of pregnancy.
1 in 5 women is having her first child after age 35 when declining egg quality can lead to infertility
The graph shows that a successful live birth of a baby is dependent on the age of the eggs used and not on the age of the mother. Women in their forties can achieve the same pregnancy success rate as women in their mid twenties if they use young donor eggs or their own cryopreserved eggs.
Unanticipated events in life can endanger a woman’s reproduction: career goals, single status, cancer at a young age, or a depleted ovarian function can all jeopardize a woman’s fertility potential.
The option available for a woman going through any of these incidences is to preserve her fertility during her youthful years (preferably age 38 years and younger) with egg freezing until she is ready for motherhood.
"Only mature, chromosomally normal eggs have a chance to become fertilized and potentially yield a pregnancy," says David Diaz, M.D., a reproductive endocrinologist and founder and medical director of West Coast Fertility Center in Fountain Valley, Calif. "Women with the greatest percentage of favorable eggs are in their 20s or early 30s." Read Article