IUI is often used to treat mild sperm problems and patients with unexplained infertility. It is also used to treat single women and female same-sex couples with donated sperm. Before performing IUI it is important to ensure that the Fallopian tubes are not blocked, or at the very least, that the risk of tubal blockage is low. This is because if tubes are blocked, sperm will not be able to reach the egg to fertilise it and IUI would be useless. IUI is also inappropriate in cases of severe sperm problems; in these cases IVF with ICSI is advised.