Most women seem to understand instinctively that fertility declines with age. The “why” of it is generally less clear. There are a number of factors that contribute to age related fertility decline, but by far the most influential is a progressive decline in what we refer to as egg/embryo “competence.” Simply put, this is the ability for any given egg/embryo to develop into a healthy baby.

To set the stage, it is important to understand that humans are poor reproducers. We only have about a 20% chance of conceiving in a given month – which translates to just a 10-12% chance of having a baby. This is largely because of the prevalence of chromosomal abnormalities within the egg that render most embryos “incompetent.” The result of these abnormalities is usually failure to conceive or early miscarriage.

Our research indicates that at least 60% of a younger woman’s eggs have inherent numerical chromosomal abnormalities (aneuploidy). By age 40, this increases to more than 80%, and by age 45, it’s likely to be well above 90%. We have also found that fertilization of an aneuploid egg will invariably produce an aneuploid (“incompetent”) embryo. It’s no wonder conception is tough!

So, how can we identify competent embryos? This really is the “holy grail” of IVF – identifying and transferring the embryo(s) that will make a baby. Most IVF laboratories use microscopic grading of embryos to assess their potential – what I call the “microscopic beauty pageant.” But examination under a light microscope cannot visualize the chromosomes – the most important factor in embryo competence. Until recently, the only method available for identifying chromosomally normal eggs/embryos was through the use of Preimplantation Genetic Diagnosis (PGD) using a process known as Fluorescence In Situ Hybridization (FISH). As it turns out, this approach has limited value because FISH only allows identification of less than ½ of the embryo’s chromosomes. What’s more, the process of PGS/FISH can damage the embryo and reduce its viability. (Read more about embryo selection).

It was not until a few years ago that a breakthrough came. It arrived in the form of a more advanced genetic test known as Comparative Genomic Hybridization (CGH) that identifies every chromosome in a cell. This test involves removing the DNA from a single embryo cell (blastomere) a few days after fertilization and subjecting it to sophisticated genetic testing. The use of CGH embryo analysis enables IVF doctors to identify the embryos most likely to be fully “competent.” In fact, a single CGH-normal embryo will, regardless of the age of the egg provider, result in a live birth more than 60% of the time (More about CGH).

This new approach, which can also be used to identify chromosomally normal eggs for selective freezing/banking, promises to revolutionize fertility preservation opportunities for women who are facing fertility-threatening cancer treatment or who desire to postpone childbearing for other personal reasons. (More about egg freezing).

In addition to an age related decline in the rate of egg and embryo “competency”, there is also the fact that as women reach their late 30’s and early forties, many will start experiencing a decline in their “ovarian reserve.” This means that in spite of aggressive stimulation with potent fertility drugs, they will produce fewer and fewer eggs until the production ceases altogether at menopause. It is the combination of declining availability of eggs and an increasing rate of egg aneuploidy that explains why reproductive performance is reduced and why it becomes increasingly more difficult to become pregnant, stay pregnant and give birth to a chromosomally normal baby as the woman ages.

Finally, there is the fact that as ovarian reserve declines, the ovaries respond differently to stimulation with fertility drugs .While one can do nothing to lower the incidence of age related aneuploidy, it is possible to avoid a further increase in egg/embryo aneuploidy through customizing protocols of ovarian stimulation to suit the needs of the individual.