An ectopic pregnancy is one in which implantation of the fertilized ovum occurs at a site other than the uterine cavity (Figure 55-1).
Tubal pregnancies are common, representing about 0.5% of all pregnancies. The incidence is believed to be increasing, possibly as a consequence of the general increase in the incidence of pelvic inflammatory disease, which causes tubal narrowing and adhesions that interfere with passage of the fertilized ovum. Endometriosis involving the uterine tube is also associated with an increased risk of tubal pregnancy. In many cases of tubal pregnancy, however, no etiologic factor is identified.
In spite of the abnormal implantation site, the ovum develops normally in the first few weeks, forming a placenta, an embryo, and an amniotic sac. Later development is greatly impeded by the lack of space, poor vascular supply, and limited placental size.
Rupture of the tube containing the pregnancy frequently occurs 2–6 weeks after fertilization, causing massive, potentially fatal intraperitoneal hemorrhage (Figure 55-2). This may occur so early in the course of the pregnancy that the patient may not have missed a menstrual period. The embryo may still be alive (in which case the pregnancy test for serum or urinary human chorionic gonadotropin (hCG) will still be positive). In most cases, the released embryo dies soon after tubal rupture. When rupture of a tubal pregnancy releases a live embryo into the peritoneal cavity, it can move to a secondary implantation site on the peritoneal surface (secondary abdominal pregnancy). Very rarely, such a pregnancy progresses to term, although of course normal delivery cannot occur.
Tubal pregnancy, showing hemorrhagic mass in the ampulla of the uterine tube. No products of conception are seen in this photograph, but they were identified on microscopic examination.
If the tubal pregnancy does not rupture, death of the embryo occurs at about 10 weeks, with one of several consequences: (1) absorption of the products of conception; (2) calcification of the fetus to form a lithopedion (Gk lithos, stone, paidion, child); or (3) extrusion of the dead fetus into the peritoneum through the fimbrial end of the tube—again associated with severe intraperitoneal hemorrhage.
Patients with tubal pregnancy present with evidence of early pregnancy such as a missed menstrual period, vomiting of pregnancy, or a positive pregnancy test. This is associated with an absence of appropriate uterine enlargement and the presence of a tender mass in the adnexa, representing the expanded uterine tube.
Rupture of a tubal pregnancy produces severe abdominal pain and intraperitoneal bleeding, often rapid and severe. The presence of blood in the peritoneal cavity can be confirmed by aspiration or laparoscopy. Many patients are in a state of hypovolemic shock at the time of presentation.
Death of the fetus in a tubal pregnancy results in rapid decline in the serum level of chorionic gonadotropin, leading to a negative pregnancy test. Decline in hCG levels causes the corpus luteum to degenerate. This leads to decreased estrogen and progesterone levels, which causes the endometrium to break down. Uterine bleeding results.
The diagnosis of tubal pregnancy is established by clinical examination. The absence of chorionic villi in endometrial curettings from a woman who appears to be pregnant requires exclusion of the presence of tubal pregnancy. Endometrial curettage is performed in a patient who shows evidence of pregnancy only when there is persistent severe vaginal bleeding. In such patients, the differential diagnosis includes spontaneous abortion and ectopic pregnancy.
The diagnosis and treatment of tubal pregnancy is urgent. Traditionally, the treatment of choice has been to remove the uterine tube on the affected side (salpingectomy). Recently, attempts have been made to save the tube (salpingostomy), particularly if bilateral tubal disease is present, in order to preserve maximal fertility. In such patients, there is a high risk of recurrence of tubal pregnancy.