Polar body diagnosis (PBD)

Genetic examination of eggs for IVF and ICSI

Each egg has the genetic material of the mother in the form of chromosomes. If the chromosomes are sequenced incorrectly, pregnancy may not occur or it may be terminated at an early stage. This applies both to pregnancies that occurred naturally as well as for pregnancies resulting from IVF. An essential factor in chromosomal maldistribution is the advancing age of a woman. Women who undergo IVF or ICSI treatment at our centres can have the chromosomal distribution of their eggs examined using polar body diagnosis. Our experience shows that with artificial insemination, PBD can reduce the risk of miscarriage.

How does polar body diagnosis (PBD) work?

PBD is carried out before artificial insemination. Before the pronuclei of the mother and the father are merged in the fertilised egg, the two polar bodies are taken from the egg – and this does not affect the development of the embryo. An examination of the polar bodies provides indirect information about the genetic constitution of the egg – among other things, whether chromosome sets are swapped (translocations), missing or appear multiple times (maldistribution). That is why PBD is also referred to as “indirect genetic examination”.

What are the differences between polar body diagnosis (PBD) and pre-implantation genetic diagnosis (PGD)?

The main difference between pre-implantation genetic diagnosis (PGD) and polar body diagnosis (PBD) lies in the time window of the examination. With PGD, embryos obtained through IVF that already consist of 4-8 cells are examined. Due to existing laws concerning the protection of embryos, many countries (e.g. in Germany) allow the use of PGD only to a limited extent. PBD is carried out in the very small window of time between fertilisation of the egg and merging of the two cell nuclei, when the fertilisation process is not yet completed. PBD is thus used for “pre-fertilisation diagnosis” and is also allowed in countries that prohibit PGD.

Another difference lies in the number of anomalies that can be detected by means of the examinations. Whereas with PGD we can now identify approximately 200 different genetic diseases and abnormalities, PBD is limited to the examination of chromosomal maldistribution. The risk of transmission of genetic diseases is thus not completely excluded with this approach.

For whom can polar body diagnosis be helpful?

• Women over 35 years

• Patients with repeated unsuccessful embryo transfer

• Women with a history of repeated miscarriages

  
  

This method is particularly suitable for patients with at least six (or preferably more) eggs. The examination can, however, also be useful in the case of a smaller number of eggs, such as for couples who have undergone several unsuccessful treatments.

As a pioneer in the field of fertility treatment, we – TFP and SH-Gen Wiesbaden – have taken a crucial step towards finding the euploid embryo: a new method of PBD makes use of “pre-implantation genetic screening” to enable reliable conclusions to be drawn about the overall chromosomal features of fertilised oocytes. Euploid eggs can be identified with certainty; selective transfer of the more developed cells increases the odds of sustaining the pregnancy.

Limits of polar body diagnosis

PBD covers only maldistribution of the mother’s chromosomes. These are the cause of over 80% of maldistribution in the embryo. Chromosomal disorders of the sperm cells or any subsequent maldistribution in the embryo go undetected. If necessary, they could be excluded in subsequent prenatal examinations.

In individual cases it may happen that not every polar body can be subjected to an analysis. Thus, the corresponding eggs cannot be definitively assessed. In such a case, our doctors decide together with the patient whether an embryo transfer should be carried out with these eggs or not – this would make the starting situation the same as it would have been without PBD.