Genetic egg-cell analysis
Another option for selecting fertilised egg cells is made possible by polar body biopsy (PBB).
Polar bodies are formed in the course of egg-cell maturation and the fertilisation process. These polar bodies contain chromosomes (carriers of genetic information) that have been separated from the egg cell. These chromosomes can be subjected to genetic testing. There are two polar bodies that are expelled as the egg cell divides during the maturation process and after the sperm has penetrated.
Polar body biopsy provides valuable information about the genetic quality of the egg cells, which show abnormalities (aneuploidies) in the distribution of chromosomes in 30 – 80% of cases, meaning that they would not usually be suitable for implantation or the birth of a healthy child.
The proportion of egg cells containing abnormalities in chromosomal distribution increases with the age of the woman. However, there are also younger patients who can have frequent cases of eggs cells with abnormalities in chromosomal distribution for no apparent reason.
How does polar body biopsy work?
The genetic-information carriers located in the polar bodies are no longer required for the further development of the cells. They are, so to speak, the waste matter of the cell, but they are also the mirror image of the remaining hereditary carrier in the egg cell, and as such they have a high diagnostic value.
In order to carry out PBD, ICSI treatment needs to be done first. Approximately 12-14 hours after ICSI treatment, the outer shell (zona pellucida) of the egg cell is opened with a laser beam under microscopic control. The first and second polar bodies are then removed using a glass capillary and made available for genetic diagnostics in the relevant centre for medical genetics and laboratory medicine.
The analysis is carried out using the so-called array-CGH (array-based comparative genomic hybridisation). This technique is based on the measurement of dose differences of the polar body DNA compared to a known reference DNA. The array-CGH technique can analyse all polar body chromosomes for abnormalities in distribution (excessive or insufficient genetic material).
- Used as part of ICSI treatment
- Genetic diagnostics in the relevant centre for medical genetics and laboratory medicine.
Limitations of polar body biopsy
- The removal of the polar bodies can result in damage to around 5% of the egg cells, which are then no longer able to develop normally. Another potential problem is that it is not always possible to remove both polar bodies. An abnormality in chromosome distribution could still therefore be present in the polar body that was not able to be examined.
- The procedure is mostly suitable for patients who have at least six or seven egg cells, preferably more. Diagnostic information is important for all patients however, (including those with a lower number of egg cells), especially for those who have previously undergone several unsuccessful courses of treatment.
- The polar body analysis only records abnormalities in chromosome distribution in the mother. Chromosomal disorders in the sperm cells or subsequent abnormalities in chromosome distribution in the embryo will therefore remain undetected. However, this procedure does reveal 80-90% of all aneuploidies in the later stages of the embryo’s development.
Polar body biopsy at KINDERWUNSCH Erlangen
Our fertility experts will be happy to help and advise you on all aspects of the polar diagnosis process and how it relates to your wish to have children.