Intrauterine insemination (IUI) using donated sperm (DI) usually has a good pregnancy rate and, if the lack of sperm is the only problem, would usually work within six cycles. Remember, though, that about 20 per cent of all couples presenting with subfertility never have a cause found for their problem. Even if all the tests on yourself have been totally normal, there may still be something undiagnosable which is reducing your fertility.
I think six cycles of IUI is certainly enough. The pregnancy rates of in vitro fertilisation (IVF) using donor sperm are much higher as the procedure bypasses many other possible blocks to fertility. It can even show where the problem lies – for example, if there is a block to fertilisation.