The cervix (often abbreviated in medical notes to Cx) is the narrow passage at the lower end of the uterus, which connects with the vagina. It allows blood to flow out of the uterus during the menstrual period, and sperm to enter after intercourse for possible fertilisation of an egg. The cervix is normally filled with mucus, the composition of which changes at different stages of the menstrual cycle. It is usually thick to stop bacteria and other infections from entering the uterus, but when an egg is released (ovulation) it becomes thinner so as to make it easier for sperm to enter and fertilise the egg. Some forms of birth control are based on a woman analysing the consistency of the cervical mucus she produces, since it is an obvious indicator of when an egg is about to be released.
When a baby is due to be born and the mother goes into labour, the canal through the centre of the cervix expands in a few hours to many times its normal diameter of about 3 millimetres up to about 10 centimetres to allow the baby out. The first stage of labour is when the muscles of the wall of the uterus start contracting while at the same time the muscle fibres of the cervix relax to allow expansion.
If the cervix opens abnormally during pregnancy, the foetus may escape and the woman will have a miscarriage. Some women have a cervix that is prone to weakness (an incompetent cervix), and if detected early enough, the cervix can be held closed by stitches, a procedure generally carried out under general anaesthetic. The stitches are removed when labour begins or at about the thirtyeighth week of pregnancy.
Sometimes the delicate cells forming the inner lining of the cervix spread to cover the tip and replace the stronger tissue normally occurring there. This is called cervical erosion and makes the cervix more vulnerable to infection. It may cause a heavy discharge and bleeding after intercourse. Generally the treatment for cervical erosion is to destroy the unwanted cells by heat (cauterisation) or laser. This is painless and usually only requires attendance at a clinic or hospital as an outpatient.
The most serious condition affecting the cervix is cervical cancer. Like most cancers, this can be effectively treated if it is detected early. The method of detection is a Pap smear, and all women should have one every two years. Deaths from cervical cancer are second only to deaths from breast cancer, but the death rate could be dramatically reduced if all women had regular Pap smears.