For many reasons, particularly since the development of the highly efficient hormonal contraceptives, the main responsibility for the prevention of an unwanted pregnancy rests with women. While many women resent this as another example of sexism, the reasons are strong.
Pregnancy occurs because a woman makes an egg (ovum) in her ovary, which develops and escapes at ovulation, to be taken into the oviduct. If a man ejaculates into the woman’s vagina within twenty-four hours of ovulation, the spermatozoa travel up through her uterus towards the oviduct, and should one reach the ovum it may penetrate its shell. This fertilizes the ovum: and pregnancy is likely.
The ejaculated spermatozoa are about eighty days old, as it has taken this time for them to be available. They are formed in ‘nests’ in the testes, and undergo several changes of shape before they enter the muscular tubes (or ducts) which connect the testes to the prostate gland. In the ducts, called the epididymis and the vas deferens, the spermatozoa become ‘mature’, and only when they are, can they fertilize the egg. The mature spermatozoa are stored in the prostate and in the seminal vesicles before being ejaculated during orgasm.