identify a good quality oocyte when initial transfer occurs, but due to DNA fragmentation in the sperm, the embryo will die after day 3 of growth. Female Genetic Abnormalities Oocyte quality is also a main contributor to overall embryo quality since it is the DNA of the oocyte that is mainly involved in the first 3 days of embryo growth following fertilization. A major source of genetic abnormalities are balanced translocations (Figure 1). A translocation involves the exchange of segments of chromosomes that are not a homologous pair. In most cases, this leads to balanced translocations, in which no DNA is lost therefore is usually asymptomatic. However, as female gametes are formed, it is probable that 2/3 of embryos produced will have unbalanced translocations within their DNA if fertilised by sperm with a balanced translocation too. Translocation mutations can occur at any point during fertilization or even the first meiotic division that the oocyte undergoes during foetal life. Zona Pellucida Dysfunction The female egg (oocyte) is surrounded by a layer of glycoproteins called the zona pellucida. Once fertilisation has occurred, this layer will harden to prevent further sperm entering and maintain the shape of the fertilized egg (zygote) as it divides to form a blastocyst (Figure 2). Once the inner cell mass - the group of cells within the blastocyst that go on to form the embryo - starts to expand, lysin enzymes secreted by the inner cell mass will act on the zona pellucida and weaken the hardened structure. Eventually, this will cause the rupture of the zona pellucida, allowing the blastocyst to hatch and begin to implant into the uterine wall. If the zona pellucida fails to thin in preparation for rupture, this will prevent the blastocyst from hatching and therefore be unable to implant, therefore this is a probable cause of repeated implantation failure (RIF). This is supported by a study which showed that implantation rates in women who received assisted zona pellucida hatching - use of synthetic chemical to artificially weaken the zona pellucida - increased. Investigations Women with RIF should undergo ovarian function testing to explore their levels of FSH, AMH and any other hormones or follicle counts which may indicate the overall behaviour of the ovarian reserve. Male partners may also be offered laboratory testing of sperm DNA integrity. In the instance of genetic testing, karyotyping may be made available to couples with RIF