Why doesn't fertility treatment always work?

Healthy eggs: The biggest reason is a problem with egg health, such as aneuploidy. Most eggs do not have the capacity to produce a pregnancy. Some have missing parts of the genetic recipe for pregnancy.

Many reasons: There are many reasons for infertility treatment failing. Human reproduction itself is a very inefficient process and even in young fertile couples only 1 in 4 or 5 attempts will result in a baby. Many couples quit before that get to the treatment they need. Apart from that, the most common reasons are abnormalities in the eggs or sperm, stress and technical difficulties related to ivf.