Lodging of the foetus at a site other than the mucous membrane lining the womb. It may become lodged in a Fallopian tube (oviduct), the ovary, the cervix or the abdominal cavity. After the sperm has fertilized the ovum in the wide mouth of the Fallopian tube, the fertilized ovum normally lodges in the womb. Currents in the uterine fluids and the rhythmic contractions of the oviduct ensure that the foetus is carried from the oviduct to the uterus. However, constrictions in the tube caused by scars or cramp may impede the smooth passage of the ovum. The presence of a receptive surface can enable the ovum to lodge itself in the oviduct. About 95 per cent of ectopic pregnancies take place in the Fallopian tube. Much less frequently (in about 5 per cent of cases), the ovum lodges itself somewhere in the abdominal cavity. The chance of an ectopic pregnancy increases slightly with advancing years and with the use of the mini-pill or the contraceptive coil. An ectopic pregnancy is also more frequent in women who have had to wait a long time to become pregnant, and in women who have previously had inflammation of their oviducts (salpingitis). Such inflammations cause scars and constrictions. Ectopic pregnancy occurs in about 1 per 200 cases. The first three months of a pregnancy of this kind frequently do not differ from a normal one; all the characteristic features are present. However, the growth of the foetus in the oviduct cannot continue undisturbed, and the duct practically always ruptures at a certain point. This process is accompanied by pain in the left or right abdomen, sometimes radiating to the upper legs or back. Direct loss of blood through the vagina need not always occur. If the woman does not realize that she is pregnant, she may regard bleeding as normal menstruation. In ectopic pregnancy, however, the loss of blood is not so great as in menstruation, but it lasts for longer, and the blood is darker in colour. The loss of blood in the abdominal cavity is a danger to life if blood vessels around the foetus in the oviduct burst. The risk of this occurring is unjustifiably high if an ectopic pregnancy goes to full term. The foetus is therefore removed by an operation when an ectopic pregnancy is detected. The oviduct is normally also removed in such cases and therefore the chances of a subsequent pregnancy are reduced. Pain in the abdomen and loss of blood in early pregnancy are always warning symptoms that require close examination.