Fertility Center Hamburg
Fertility Center Hamburg

The role of the genetic make-up of egg cells in fertility

The genetic make-up of egg cells plays a crucial role in the success of pregnancy. As women get older, however, the number of their egg cells with chromosome maldistributions increases. Embryos developing from these defective egg cells often do not implant in the uterus, or, even more problematically, cause early miscarriage. Studies have shown that approx. 70-80% of egg cells in 40-year-olds have chromosomal abnormalities. Few embryos with chromosomal maldistributions achieve viability. The most common of these chromosomal anomalies is trisomy 21, also known as Down syndrome.

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

PBD was developed to detect egg cells with chromosome maldistributions and distinguish them from healthy egg cells, so that only embryos arising from normal egg cells are transferred into the uterine cavity. This method is thus particularly suitable for women over 35, but also for women who have had several miscarriages or failed fertility treatments.

Polar bodies are byproducts formed during the egg cell maturation process and fertilisation. They contain the chromosomal material not required for the later development of the embryo. Polar bodies contain a mirror image of the genetic material in the egg cell - and can thus serve as indicators for maldistributions.

There are two technical approaches for analysing the chromosomes in a polar body after its removal from the fertilised egg cell. The older method, which has now become outdated, is FISH (fluorescent in situ hybridisation). Here, the eight chromosomes most frequently affected (X, 13, 15, 16, 17, 18, 21, 22) are tested for maldistributions. This is done using special probes that bind to these chromosomes and make them visible under the microscope. Using this technique, at best approx. 80% of possible chromosome maldistributions can be diagnosed. But the number of tests that give no meaningful diagnosis is rather high.

FCH was the first fertility clinic in Hamburg to establish PBD in 2003, and has successfully carried out the procedure thousands of times since then. Since 2012, FCH offers the more complex chip analysis method called array comparative genomic hybridisation (aCGH). With this technique, all human chromosomes can be analysed (not just the 8 most commonly affected ones), the analysis of individual chromosomes is much more precise, and chromosome translocations in women can be diagnosed (this is the exchange of pieces of DNA between non-homologous chromosomes). This configuration can be inherited, but also leads to a much higher risk of miscarriage in affected women. Overall, the aCGH technique gives more comprehensive results, but is more expensive due to the more sophisticated technology.

When is PBD useful?

In the sense of the German Embryo Protection Act, PBD studies the recently fertilised egg cell. This is not yet an embryo, as the maternal and paternal genetic material has not yet merged. PBD on egg cells thus only investigates the chromosomes from the mother, meaning that the results do not apply to the father’s genetic material. However, the sperm cells can also be tested in advance for chromosome maldistributions where necessary, using the FISH technique. PBD is possible with both IVF and ICSI treatments. Deciding to carry out PBD is a very individual question for each couple. If you are unsure, don’t hesitate to discuss this openly with your doctor. Here, we can only give a few very general recommendations:

From around 35 years old, PBD is a worthwhile test method, as the number of chromosome maldistributions clearly increases in women aged over 35. Using PBD increases the chances of a normal pregnancy. Younger women may benefit too, if they have not become pregnant after two or three rounds of IVF or ICSI treatment, or if pregnancy has ended in miscarriage. These patients often have elevated rates of chromosome malformations. PBD helps to improve the selection of normal, healthy egg cells and thus can lead to higher pregnancy and birth rates.