The role of the oocyte in fertility

With a woman’s advancing age the number of oocytes with chromosome malsegregations increases. Embryos developing from these so-called unbalanced or aneuploid oocytes often do not implant in the uterus, or, if they implant, are more likely to cause early miscarriage. Polar body diagnosis is a method particularly suitable for women over 35 years of age, but also for women who have had several miscarriages or failed IVF/ICSI treatments. The latter cases are often signified by an increased rate of chromosome malsegregations independent of the woman’s age.

The number of oocytes with chromosome maldistributions increases with age. With polar body diagnosis (PBD), we can exclude these from transfer.

In the course of IVF/ICSI treatment, PBD allows genetic analysis of oocytes with respect to chromosomal malsegregations (aneuploidies). The aim of the diagnosis is to increase the birth rate and reduce the risk of miscarriages.

Polar bodies arise as nuclear by-products of meiosis during the oocyte maturation process. They contain chromosomal material not required for the later development of the embryo. After hormonal ovarian stimulation, follicular puncture and in vitro fertilisation of retrieved oocytes, both polar bodies are biopsied from fertilised oocytes. By means of specialised technical approaches – array-CGH (comparative genomic hybridisation) or NGS (next generation sequencing) – the presence of the 23 different human chromosomes in both polar bodies is examined. This allows inference of the chromosomal composition of the fertilised oocyte. Only oocytes with the correct number of chromosomes are then selected for further development and later embryo transfer. This increases the chances for an intact pregnancy.

PDB not only allows detection of numerical malsegregation of whole chromosomes, but also of unbalanced structural chromosomal disorders. Therefore carriers of balanced structural chromosomal disorders, such as translocations or inversions, also benefit from PDB. This applies in particular to women suffering from habitual abortion or who have given birth to a child with an unbalanced chromosomal disorder.

In Germany, PDB is a legal diagnostic means in conformity with the German Embryo Protection Act and the Genetic Diagnosis Act. Furthermore, current knowledge suggests that taking the biopsies for PDB does not negatively impact normal development of the embryo.