20 June 2006
ByAppeared in BioNews 364
Italian scientists have presented research at the annual conference of the European Society of Human Reproduction and Embryology (ESHRE) in Prague, Czech Republic, showing that eggs can be screened - before they are fertilised - for chromosomal abnormalities that might reduce IVF success rates.
Ana Pia Ferraretti and colleagues, from SISMER (Societa Italiana Studi di Medicina Della Riproduzione) in Bologna, Italy, looked at chromosomes contained in the 'first polar body' - a small cellular structure, surrounded by a membrane, that is expelled from the developing egg during cell division and which contains the same number of chromosomes as the egg. By doing this, they found they could select healthy eggs with the correct number of chromosomes. Some eggs, particularly in women over the age of 35, are 'aneuploid' - that is, they contain the wrong number of chromosomes. Aneuploidy can result in miscarriage or birth defects - one of the most well known aneuploidies is trisomy 21, which causes Down syndrome.
The researchers studied 266 women implanted with embryos created from eggs fertilised after the analysis of the first polar body (PBA). They compared these with a control group of 244 women implanted with eggs that had been selected because their external appearance was normal. In the PBA group, they tested the first polar body for five chromosomes that are commonly associated with aneuploidies connected to miscarriage: chromosomes 13, 16, 18, 21, and 22. They round that the rate of early miscarriage was significantly lower in the women whose eggs had undergone PBA: only 11.5 per cent of these women experienced miscarriage, compared to 28.6 per cent of women in the control group. The researchers also found that performing PBA had no effect on fertilisation rates, embryo development or implantation potential.
Italy's laws on human fertilisation and embryology, passed in December 2003 and said to be the most restrictive in Europe, were passed to counter the country's reputation for being the 'Wild West' of fertility treatments. The law restricts the provision of fertility treatments to 'stable heterosexual couples' who live together and are of childbearing age, and who are shown to be clinically infertile. Research using human embryos is prohibited, as well as embryo freezing, gamete donation, surrogacy, and the provision of any fertility treatments for single women or same-sex couples. The law also says that no more than three eggs can be fertilised at any one time, and that any eggs fertilised must all be transferred to the uterus simultaneously, increasing the risk of multiple births. PGD (preimplantation genetic diagnosis) and prenatal screening for genetic disorders are banned.
As Italian doctors are banned from discarding or freezing surplus embryos, this new research may go some way to helping infertile women in Italy. 'As a consequence [of the law], a maximum of three oocytes (eggs) have to be selected for insemination in order to avoid the development of more than three embryos', explained Ferraretti. 'However, the three chosen might not be the best oocytes and, especially in women over 35, there is a very high chance of choosing aneuploid oocytes, which consequently will develop into embryos that either fail to implant or are more likely to miscarry at a later stage', she added. The researchers plan to continue tests to assess the safety of the procedure and to test other chromosomes that may have links to problems in early embryo development or implantation, independent of the woman's age. 'If and when we are able to have the full information on an oocyte's chromosome competence, assisted reproductive technology will become more efficient', Ferraretti said.