When you want to know how long it takes for the fertilization after an IUI, you must know what is an IUI. IUI is when a semen sample is not as effective, it has a little low count and the motility is low. So the semen sample is washed . There are different techniques of washing. After washing the semen sample, when the egg has ruptured, we inseminate the girl with the semen sample . This is IUI. It takes atleast 15 days for somebody to know that they are pregnant after IUI. What happens is once IUI is done. The patient feels that the patient is pregnant, it is not that. It takes 15 days for the pregnancy test to come positive in a urine sample. Even in a blood sample you have to cross your dates for the pregnancy to come positive. What happens after IUI is the sperm enters the uterine cavity. The egg from the fallopian tubes is gradually coming towards the uterus and then there is fertilization of this and then implantation of the embryo into the uterine cavity. Only after implantation occurs does the pregnancy test come positive. That is why we have to wait for 15 days after an IUI to know whether you are pregnant. So you don’t expect a pregnancy immediately on the same day after an IUI or the next day after IUI.