Ectopic pregnancy occurs when a fertilised ovum implants somewhere other than the uterus. In 99% of cases, the site of implantation is in one of the Fallopian tubes1. This might be due to a delay in the passage of the ovum along the tube, but the underlying mechanism of ectopic pregnancy is still not properly understood. It is, however, known that women who become pregnant during oral contraceptive use or fertility treatment, or following sterilisation, have an increased risk of ectopic pregnancy. Chlamydia infection, which can scar the tubes, also increases the risk of an ectopic pregnancy. The resulting symptoms include a lack of periods, abdominal pain or tenderness, and vaginal bleeding. Around 1% of pregnancies are affected, but maternal deaths are rare in developed countries.
Miscarriage and Rupture
The common outcomes for an ectopic pregnancy in the Fallopian tube are tubal abortion2 and rupture. Around 65% of ectopics abort, usually during the sixth to tenth weeks of pregnancy, with multiple small bleeds at the point of implantation causing the ovum to detach from the tube wall. This is followed either by absorption of the ovum, in which case there are no further problems, or obstruction and distension of the tube by the clot-covered ovum. Rupture of the tube wall occurs in around 35% of cases, usually around the time of the first period missed due to the pregnancy, and is due to the ovum having burrowed into the outer layer of the tube. This leads to bleeding into the abdominal cavity or the broad ligament3, depending upon the direction in which the rupture occurs.
One alternative to tubal abortion or rupture is the vanishingly rare phenomenon of abdominal pregnancy. In this case, the ovum remains connected to the wall of the Fallopian tube and later attaches itself to the organs surrounding the uterus. A small number of abdominal pregnancies actually survive to reach full term, and a smaller number still die midway through growth to form a lithopaedion. A lithopaedion, or 'stone baby', is a foetus that has died and become calcified on the outside to keep it separate from the living tissue of the mother. Lithopaedia may remain unnoticed for many years, and are a staple of disreputable novelists.
Ectopic pregnancy can cause a range of symptoms, and needs to be considered by doctors in the diagnosis of any woman of childbearing age presenting with abdominal symptoms. Abdominal pain or tenderness occurs in most ectopic pregnancies, but may occur on defecating or passing urine and can thus be mistaken for constipation or urinary tract infection.
In cases with a slow onset, a lack of periods due to the presence of a pregnancy is followed by mild pain not dissimilar to that experienced during early pregnancy. Attacks of sharp pain and faintness due to bleeding into the abdomen occur infrequently, and may be accompanied by vaginal bleeding. This bleeding is slightly brown in colour but may be mistaken for menstruation or a miscarriage. These attacks continue until the woman either suddenly becomes acutely unwell due to obstruction or rupture of the tube, or the symptoms resolve following a successful tubal abortion.
As the above may be mistaken for normal symptoms of pregnancy, it is not unusual for the first indication of an ectopic to be the sudden, severe abdominal pain that follows tubal rupture. This pain is severe enough to cause fainting, and is accompanied by an internal haemorrhage leading to collapse, a rapid heart rate and falling blood pressure. The haemorrhage tends to improve soon after onset, but the pain continues and may spread to the stomach or the shoulder. Another haemorrhage may soon follow, and so urgent diagnosis and treatment is required.
In sudden onset cases, the diagnosis is usually clear. In slow onset cases, a urine dipstick and blood test for β-hCG4 may be performed. If this is negative, pregnancy of any sort can be ruled out; if it is positive, a transvaginal ultrasound scan should be performed to look for an empty uterus and the presence of a foetus in one of the Fallopian tubes. The presence of a foetus in the uterus on ultrasound makes a co-existing ectopic pregnancy extremely unlikely; in all other cases, treatment by laparotomy or laparoscopy is considered5. Further blood tests to measure β-hCG and progesterone levels may help if the diagnosis is uncertain.
Patients with suspected ectopic pregnancy are transferred to hospital and provided with intravenous fluids and pain relief as required. Once the diagnosis has been confirmed, the ectopic may be removed either through a laparotomy or laparoscopy, the latter being preferred as it leads to less blood loss and a quicker recovery. The tube containing the ectopic may either be removed (salpingectomy) or cut open to remove the ectopic (salpingostomy). In cases where the implanted ovum is still small and the tube has not ruptured, the drug methotrexate may be injected into the ectopic or given by injection to the patient. If this treatment is used or a salpingostomy is performed, β-hCG blood tests are performed weekly to ensure that the treatment has been successful.
As mentioned earlier, very few women in developed countries die from ectopic pregnancies. However, ectopic pregnancy may result in infertility, and some women who have suffered an ectopic choose not to become pregnant again. The risk of having a second ectopic is around 10%, and so women with a past history of ectopic pregnancy are followed carefully in subsequent pregnancies.
1 Also known as oviducts, these are a pair of tubes that lead from the ovaries to the uterus.
2 This refers to the spontaneous ending of an ectopic pregnancy, and is not to be confused with the common usage of the term abortion, which refers to the intentional termination of a pregnancy.
3 The broad ligaments are sheets of tissue hanging from the Fallopian tubes and attached to the sides of the uterus.
4 β-human chorionic gonadotrophin, a hormone produced by the implanted ovum, which is thus present in the blood of pregnant women.
5 Laparotomy involves opening the abdomen through a large surgical incision, whereas laparoscopy involves the use of several small 'keyhole' cuts through which a camera and surgical instruments can be passed.