During natural conception, only the hardiest sperm manage to travel great distances and break through the membrane of an egg to fertilise it. Weaker sperm don't make it. But because ICSI bypasses this natural selection process, there's an increased risk of rare genetic problems carried by the sperm being passed on to the child. Some but not all genetic problems can be tested for before you have the treatment.
http://www.babycentre.co.uk/a4097/fertility-treatment-intracytoplasmic-sperm-injection-icsi#ixzz3ZK6Pb6AJ