Aneuploidy in oocytes is known to be one of the main contributors to unsuccessful ART cycles, especially in women aged ≥38 years. Several factors, including maternal age, have been attributed to the occurrence of around 50% of the chromosomal aneuplodies. Researchers from the University of Oxford have now developed a new, less-invasive, genetic test for chromosomal analysis of polar bodies with comparative genomic hybridization (CGH), in order to improve the pregnancy rates in older women with multiple failed IVF cycles. The results of the study were presented at the 25th annual conference of the European Society of Human Reproduction and Embryology held at Amsterdam, from June 28 to July 1, 2009.
Elpida Fragouli and colleagues from the Department of Obstetrics and Gynaecology, University of Oxford, UK, and Reprogenetics, UK, conducted the study by evaluating 400 fertilized eggs obtained from women (mean age of 42 years) with poor reproductive history. The poor reproductive history in these women were attributed to the chromosomal aberrations found in >50% of all the oocytes, which could in turn lead to chromosomally abnormal embryos.
CGH was used to analyze the oocytes by examining the polar bodies, which are by-products of the meiotic cell cycle during egg development. Evaluation of the chromosomes of the polar bodies would indicate if the corresponding oocyte would be normal. Using this test, the researchers achieved a 20% pregnancy rate in the study subjects (n=35), which is almost double the usual rate observed in women with poor prognosis. They further reported 2 live births in this group till date, with all others maintaining their pregnancies.
Based on the findings, the investigators reported that this new, less-invasive genetic test has the potential to improve the success rates of IVF in older women with repeated ART failures. It may also facilitate in reducing the frequency of spontaneous miscarriage and the occurrence of congenital anomalies such as Down syndrome. The scientists further proposed to
• apply various technical innovations to the test to make it better, less expensive, and faster
• use the test also in patients requiring fertility preservation, as in cancer patients, to preserve competent oocytes
The last 10 years have seen the emergence of new preimplantation genetic diagnostic techniques in the field of assisted reproduction that help enhance treatment outcomes. Polar body diagnosis, an indirect genetic analysis of oocytes, may serve as an ethically acceptable substitute to preimplantation genetic screening. Some of the advantages of CGH for polar body diagnosis, over the conventional screening techniques such as fluorescent in situ hybridization (FISH) include:
• Evaluates the whole complement of chromosomes
• Less invasive
• No adverse effect on the subsequent embryo development with the removal of polar bodies
• More accurate, as the presence of chromosomal mosaicism does not negatively influence the results of CGH
Additionally, the innovative genetic test holds significant application in countries where the screening of embryos is forbidden and enhances the use of single embryo transfer with its ability to select high-quality oocytes.
References
1. New, less invasive genetic test greatly improves pregnancy rates in older women with poor prognosis. Press Release. ESHRE. Last Accessed July 13, 2009.
2. Buchholz T, Klehr-Martinelli M, Seifert B, Bals-Pratsch M. Polar Body Analysis – Current Clinical Practice and New Developments for Preimplantation Genetic Screening and Diagnosis. J Reproduktionsmed Endokrinol. 2009;6(1),32-34.
