This technique consists of introducing motile sperm (the fertile fraction of semen) into the uterus. Motile sperm are isolated from the other components of semen, i.e., seminal plasma and other cells. Ovulation is gently stimulated in order to increase the effectiveness of artificial insemination (AI). This helps the woman become pregnant without producing a multiple birth. It is a simple technique involving at least two million motile spermatozoa, although it cannot be performed if the woman has tubular obstruction. Success rates are 15 to 20% per cycle. If pregnancy does not occur after 3 cycles, it is suggested the couple try in vitro fertilization.