Couple Fertility
Sperm ejaculated into the vagina will normally die in its acidic environment in a few hours or less. In the days preceding ovulation however, a woman’s cervix (which is at the base of the uterus) produces specialised mucus which can nourish and sustain the sperm for up to five days. This mucus is also important for the filtering of abnormal sperm and the transportation of healthy sperm into the uterus (Fig. 1a).
Oestrogen from the ovary causes the cervix to produce specialised mucus (main figure: blue, white) immediately prior to and during ovulation. Healthy sperm swim through this mucus at the cervix into the uterus, while many abnormal sperm are trapped in it.
Of the several hundred million sperm deposited into the vagina during ejaculation, only around 200 will reach the ovum, and only one will be able to fertilise it. Once ovulation has occurred, the specialised mucus is no longer required and the woman’s hormones cause the cervical mucus to change and her resting body temperature to rise about 0.2°C. If the ovum is fertilised, the newly formed embryo begins to develop and will implant in the soft nutritious lining of the woman’s uterus, reaching birth some 8½ months later. If there is no fertilisation, the woman’s uterus sheds the lining it had prepared for an embryo in what is known as menstruation or a ‘period’.
After ovulation, the hormone Progesterone stimulates the production of a different mucus (green) that is impenetrable to sperm.
