Fertilisation in humans is practically feasible only if

Fertilisation in humans is practically feasible only if the ovum and sperms are transported simultaneously to ampullary- isthmic junction of the fallopian tube.

During copulation (coitus) semen is released by the penis into the vagina (insemination). The motile sperms swim rapidly, pass through the cervix, enter into the uterus and finally reach the ampullary region of the fallopian tube. The ovum released by the ovary. It is transported to the ampullary region where fertilisation takes place. Fertilisation can only occur if the ovum and sperms are transported simultaneously to the ampullary region. This is the reason why not all copulations lead to fertilisation and pregnancy.