AETIOLOGY

The aetiology of most cases of ectopic gestation is not known. Implantation of the fertilized ovum can only take place when the zona pellucida has partially or completely disappeared. Premature implantation could occur if the passage of the fertilized ovum along the Fallopian tube is delayed because of tubal damage following infection. Premature implantation may occur in:

Fig. 12.1 Sites of ectopic gestation implantation, with the relative frequency of occurrence.

OUTCOME FOR THE PREGNANCY

In most cases the pregnancy terminates, in one of several ways (see below), between the sixth and 10th weeks.

Tubal abortion

This occurs in 65% of cases and is the usual outcome in fimbrial and ampullary implantation (Fig. 12.2). Repeated small haemorrhages from the invaded area of the tubal wall detach the ovum, which dies and:

• Is absorbed completely

• Is aborted completely through the tubal ostium into the peritoneal cavity

• Is aborted incompletely, with the result that the clot-covered conceptus distends the ostium

• Forms a tubal blood mole.

Fig. 12.2 Sequelae of tubal abortion.

Tubal rupture

This occurs in 35% of cases and is more common when the implantation is in the isthmus. Whereas the rupture of the ampulla usually occurs between the sixth and 10th weeks, rupture of the isthmus occurs earlier, frequently at the time of the first missed period. The trophoblast burrows deeply and eventually erodes the serosal coat of the tube, the final break being sudden or gradual. Usually the ovum is extruded through the rent and bleeding continues. If the rupture is on the mesenteric side of the tube, a broad ligament haematoma will form (Fig. 12.3).

Fig. 12.3 Sequelae of tubal rupture.

CLINICAL ASPECTS

The possibility of an ectopic gestation should always be considered in a woman of childbearing age, especially if there is a past history of acute salpingitis. The history (Box 12.1) is of greater importance than the physical signs, as these can be equivocal. Usually there is a short period of amenorrhoea, although in 20% of cases this may not be present. The pain is lower abdominal in site, but not distinguishable from that of abortion. However, in ruptured ectopic gestation fainting usually occurs, although this may only be momentary. Vaginal bleeding follows the pain, and may be mistaken for bleeding due to a delayed menstrual period or an abortion. The bleeding is a slightly brownish colour and continuous, and clots are rarely present (Table 12.1).

Table 12.1 Symptoms and signs in ectopic gestation

Two clinical patterns occur, and are due to the extent of the damage to the tubal wall by the invading trophoblast. The first is subacute, the second acute.

DIAGNOSIS

Although in acute cases the presence of internal bleeding is obvious and the diagnosis not in doubt, in subacute cases the diagnosis can be extraordinarily difficult. Laboratory tests may help, but in most instances they are not particularly informative. A radioimmunoassay for serum levels of β-human chorionic gonadotrophin (β-hCG) should be made. A negative result (<5 IU/mL) indicates that the woman is not pregnant, and ectopic gestation can be excluded. If the β-hCG test is positive a pelvic ultrasound examination should be performed, preferably using a transvaginal probe. A fetal heartbeat should be detectable once the β-hCG level reaches 1500 IU. If this shows an empty uterus (Fig. 12.4), and particularly if it shows a sac and fetus in the Fallopian tube, the diagnosis is certain. and treatment should be commenced. If the ultrasound is equivocal serial measurements of β-hCG should be taken. The levels should double every 48 hours, a rise less than 66% being suggestive of an ectopic gestation. On the other hand, if ultrasound shows an intra-uterine pregnancy, a concurrent ectopic pregnancy is extremely unlikely. Routine serum progesterone levels can help to exclude an ectopic pregnancy (>79 nmol/L) and identify a nonviable pregnancy (>15.9 nmol/L).

Fig. 12.4 Ectopic pregnancy.

If ultrasound is not available, or is equivocal, the presumptive diagnosis should be confirmed by laparoscopy.

The diagnosis of suspected ectopic gestation is summarized in Figure 12.5.

Fig. 12.5 Algorithm for diagnosis of suspected ectopic gestation.

TREATMENT

If an ectopic gestation is suspected the patient should be transferred to hospital without making a vaginal examination. If she is in shock, an intravenous line should be set up and transfer quickly arranged. Morphine may be given if the woman is in pain.

As mentioned, if there is any doubt about the diagnosis a pelvic ultrasound examination should be carried out to establish whether the pregnancy is intra- or extra-uterine.

Once the ectopic gestation has been diagnosed, the treatment is usually surgical or in selected cases medical. Several approaches are possible. The gynaecologist may:

Following conservative surgery, or if methotrexate is used, the woman should have serum hCG measurements made weekly until negative. If the woman complains of continuing symptoms, a second-look laparoscopy may be necessary.

PROGNOSIS

Less than 60% of women who have had an ectopic gestation become pregnant again. Three-quarters of these voluntarily avoid pregnancy, and one-quarter are involuntarily infertile. In a subsequent pregnancy the risk of a second ectopic gestation is 10–20%, compared to a risk of 1% in other women. Because of this, a woman who has had an ectopic gestation should be monitored carefully in the early weeks of her next pregnancy, a transvaginal ultrasound examination being made at 6–8 weeks’ gestation to establish that the pregnancy is intra-uterine.