Age is the number one predictor of fertility. It is a significant factor that can affect conception in various ways. Older women have a more difficult time becoming pregnant. Women are born with a certain number of eggs. Over time, the number and quality of eggs decreases. When a woman is younger, it is much easier to become pregnant. This is solely due to the quality of the egg.
Some tests are used to predict what is called “Ovarian Reserve.” These tests are indirect measures of the number of the eggs you may have in your ovaries. Many studies have found that a drop in pregnancy rates significantly occurs after 35 years of age and drops dramatically after 38 years of age. The quality of the oocytes drops dramatically as age increases. The percentage of genetically abnormal eggs is thought to increase as age increases.
This increase in abnormal oocytes leads to an increase in embryos with an abnormal number of chromosomes. Chromosomes are where our genetic material is stored. Every human is composed of cells possessing 23 pairs of chromosomes. One set comes from the sperm and one set comes from the egg. The architecture inside the egg at fertilization must bring these pairs of chromosomes together just right. As we get older the architecture inside the cell becomes older and sometimes does not align these chromosomes with as much accuracy as it did when the eggs were younger, resulting in an increase in the number of embryos that have what is called “aneuploidy,” or an irregular number of chromosomes. The most well-known form of aneuploidy is Down’s Syndrome, which is a normal complement of chromosomes, 23 pairs plus an additional number 21 chromosome, called Trisomy 21, or 3 copies of the number 21 chromosome. Aneuploidy also decreases the rate of implantation of embryos, which reduces fertility rates as well as increasing miscarriage rates.