They effect implantation rates by altering the shape and cytokine composition of the uterus. Removal of submucosal fibroids has shown to increase implantation rates. Endometrial polyps are benign tumours found in the endometrium which factor into female infertility. There has been limited research into if their removal increases the chances of implantation and pregnancy. Intrauterine adhesions (Asherman's Syndrome) occur from scar tissue within the uterus which cause the closure of part or all of the uterus. The adhesions prevent embryos from implanting by reducing the surface area and decreasing the receptivity. Intrauterine adhesions normally occur after damage has been caused to the endometrium, either through removal of unwanted pregnancies, miscarriage, infection, and surgical damage. Thrombophilia is a condition which makes the blood more likely to clot and this increases cardiovascular risk, meaning the individual is at higher risk of heart attacks, strokes or DVTs . In pregnancy it can lead to a disruption in the flow of blood to the placenta and the uterus wall. This can lead to a decreased receptivity of the uterus wall for a pregnancy and can lead to a miscarriage further on. However, how significantly this contributes to RIF is not fully known but each case should be assessed on a personal basis by a clinician   The successful implantation of an embryo not only relies on a receptive uterine environment in the mother but also on the quality of the embryo itself. Embryo quality and probability of implantation can be affected by maternal and paternal genetic abnormalities as well as zona pellucida dysfunction and poor embryo transfer technique. The quality of the sperm that fertilizes an egg is a key contributor to the overall quality of the embryo. Abnormalities in DNA fragmentation and chromosomal arrangements are the main source of genetic deviation in males that can affect embryo quality. DNA fragmentation occurs when the strands of DNA are separated to form two separate strands, this disrupts the genetic information that is coded in genes. Depending on the severity of the fragmentation, this can lead to the dysfunction of specific genes which may or may not be essential for embryo survival and in this case the initiation of implantation. DNA fragmentation can happen spontaneously in cells that undergo programmed cell death (apoptosis) where DNA is broken apart by enzymes called endonucleases. However, since the male DNA isn't activated until around day 3 after fertilisation, it is often difficult to diagnose sperm genetic abnormalities because morphological studies could 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.