When a woman is ovulating, sperm from her male partner or a sperm donor is prepared and inserted into the uterus. The hope is that this will give the sperm a greater chance of finding its way through the fallopian tubes to fertilize the waiting egg.

IUI depends on the sperm's ability to fertilize an egg within the uterus, so it's important that sperm function well with regard to number, movement and shape. To facilitate this, sperm are often washed (sperm washing) and concentrated in a sterile medium, which is then injected directly into the uterus. IUI is also often supported by ovulation that is induced by fertility medications (ovulation induction). The chance of achieving pregnancy with IUI is from 10% to 20% per cycle depending upon the problem.