Abstract:
Infertility is a growing medical concern in New Zealand and around the world, and is often treated using IVF and other assisted reproductive technologies. Selection of the best quality embryo to transfer in IVF is currently based on embryo morphology. There is a need for a non-invasive, quantitative biomarker which may be used to select which embryo to transfer, which may reduce time to pregnancy for couples. Cell free DNA (cfDNA) has recently been detected in embryo culture media. This DNA is nuclear and mitochondrial. CfDNA is used clinically in prenatal diagnosis of diseases such as Down syndrome, and there is potential for it to be used as a biomarker of embryo quality at the pre-implantation stage also. The aim of this study was to isolate and quantitate nuclear and mitochondrial cfDNA from embryo culture media. This could then be correlated with aspects of the embryos development to identify whether it is representative of the quality of the embryo. These included embryo quality based on morphology, fragmentation, method of fertilisation, day of embryo development, and the type of culture media the embryo developed in. We hypothesised that poor quality embryos would contain greater amounts of cfDNA in their surrounding media. Nuclear DNA was detected in 53% of samples, and mitochondrial DNA in 80% of samples in this study where n=126. There was a trend for good quality embryos with less fragmentation to have greatest mtDNA:nDNA ratio released into their surroundings. The reasons for and mechanisms of DNA extrusion are not fully understood. Possibilities include a self-repair mechanism, release during cell-cleavage, passive release, a result of cell death by either apoptosis or necrosis, or as a by-product of fragmentation. Good quality embryos may contain more mitochondria initially, which provide energy to the developing organism and so release more mtDNA copies into their surroundings. Poor quality embryos may contain less mitochondria, mtDNA, and therefore less expendable energy. Understanding the mechanisms of DNA extrusion would better allow this DNA to be used as a non-invasive, objective biomarker of embryo quality, and allow selection of the best quality embryo for transfer.