In IUI cycles, fertilization takes place in the Fallopian tubes. For this reason, it is necessary that the tubes are not blocked. If theey are blocked they would be unpassable for both the sperm and the egg, or indeed the fertilizeed embryo on its way to the uterus for implantation.
In short, tubal patency is necessary for a pregnancy to be possible.
It is also necessary that ovulation occurs with normality, that is, that an egg is released by the ovary so that the sperm can meet it in the tube.
Finally, it is crucial that sperm meet a minimum quality standard in order to be able to swim toward the tubes and be able to cause egg fertilization.