How does fertilization occur?

After a man and a woman have had sex, about 300 million sperm cells are present in the woman’s vagina. The sperms swim forward with the help of their tails with a common aim: to fertilize the egg cell. The egg cell ripens in the ovary of a woman only once a month. Certain hormones then trigger ‘ovulation’, in which the egg cell is released from the ovary in the fallopian tube. Fertilization occurs if the egg cell meets a sperm. Doctors assume that after ovulation, an egg cell can be fertilized for a maximum of 12-24 hours. A single sperm cell is enough to fertilize the egg cell.