Women, unlike men and most other living species, outlive their reproductive lifespan by many years. As the end of this reproductive life approaches - at the menopause - the store of eggs in the ovary (known in their earlier stage as follicles) declines and menstrual cycles become more irregular. Fertility too begins to decline, and studies of both natural and assisted conception suggest this decline begins after the age of 35. UK figures from the HFEA, for example, show that IVF live birth rates in women aged 34 and under were about 33% per started treatment, in women aged 38-39 around 21%, and in women aged 40 and over less than 14% and declining rapidly.
So one explanation for this decline in female fertility is the steady reduction in ovarian reserve, which can be estimated in levels of AMH and numbers of follicles. But there are also other reasons, one of which is the quality of the egg – and therefore the quality of the embryo after fertilisation.
Studies analysing the genetic and chromosome make-up of eggs and embryos have consistently found that the rate of defects increases with age, such that more than 50% of embryos might be affected. This is most clearly illustrated in the increasing risk of Down’s syndrome found in older mothers.
Down's syndrome is a condition caused only by an abnormality in which there is an extra copy of chromosome 21 (three copies of the chromosome rather than two). In some rare cases the result of an extra or missing chromosome is an inherited disease or abnormality, in others a chromosomal defect might prevent the embryo from implanting in the uterus (whether in natural or assisted conception).
As seen in the graph, the rate of chromosome abnormality increases as the implantation rate decreases. This is mainly why embryo screening for chromosome abnormalities has become more and more important, especially in women of an older maternal age.
It is for these reasons that embryo screening for chromosome abnormalities has become more and more important, especially in women of an older maternal age. The London Women's Clinic is able to provide a full range of embryo screening services.