In the USA, ectopic pregnancies are reported events. This allows some tabulation of incidence rates and outcomes.
The Centers for Disease Control (CDC) examined ectopic pregnancies occurring during the 17 year period between 1970 and 1987 and noted that the
ectopic pregnancy rate increased almost 4 fold (from 4.5 per 1000 pregnancies to 16.8 per 1000 pregnancies).
During this same time period, the
fatality rate from ectopic pregnancies dropped almost 90% (from 35.5 per 1000 ectopics to 3.8 per 1000 ectopics).
Despite the sharp improvement in the fatality rate by the end of this period of time, ectopics were still the second leading cause of maternal mortality in the USA (accounting for 12% of all maternal deaths in 1987).
The reason for the increase in ectopic pregnancy during this time period is not entirely clear. Of the known risk factors, it is believed that an increased number of cases of sexually transmitted disease (which damage fallopian tube transport of embryos into the uterus) are responsible for a significant portion of the increased number of cases of ectopic pregnancy.
Risk factors for ectopic pregnancy that should be recognized include:
- a prior history of ectopic pregnancy. When an ectopic pregnancy in the fallopian tube is treated conservatively (by preserving the tube), there is a roughly 10 fold increase in ectopic pregnancy.
- a history of surgery on the fallopian tubes or within the pelvis. When a bilateral tubal ligation (tubes tied) is followed by either an unexpected pregnancy (failed tubal ligation) or is "reversed" with a tubal reanastomosis (tubal reconstruction) there is an increased risk of a tubal ectopic pregnancy. When a woman has a history of pelvic surgery that is associated with significant adhesion formation (such as myomectomy) there is also an increased risk of an ectopic pregnancy.
- a history of pelvic infection. Salpingooophoritis, or Pelvic Inflammatory Disease (PID), is particularly destructive to the fallopian tubes. Chlamydia (a common sexually transmitted disease) and Gonorrhea are both able to grow within the fallopian tubes and cause tremendous damage to the endosalpinx (lining of the inner tubal lumen), agglutination (sticking together) of the mucosal folds in the tube, and peritubal adhesions (scar tissue). The increased risk of an ectopic pregnancy is greater with an increased number of pelvic infections. It also appears that the risk of an ectopic pregnancy is greater when the woman with the infection is younger (possibly related to avoiding or otherwise delaying appropriate medical care). Other pelvic or lower abdominal infections can also result in pelvic adhesions and an increase in the ectopic pregnancy rate (such as appendicitis).
- use of assisted reproductive technology (such as IVF and GIFT). When multiple embryos or gametes are replaced into the uterus or the fallopian tubes, the risk for multiple pregnancy rises significantly. The risk of a heterotopic pregnancy (twins with one pregnancy in the uterus and one in the fallopian tube) is generally thought to be about 1 in 30,000 pregnancies in an unselected population. This incidence rate was determined in 1948 by using the rates of dizygotic twins and ectopic pregnancy at that time. At this time, the rates of both ectopics and dizygotic twins have increased and the rate of heterotopic pregnancy is more likely about 1 in 10,000 to 1 in 15,000 pregnancies. In women conceiving with one of the assisted reproductive technologies (ARTs) the incidence of heterotopic pregnancy may increase to as frequently as 1 in 100 pregnancies since multiple gestation is much more common and the hormone concentrations achieved may enhance tubal implantation.
- a history of IUD use. The use of an IUD is a classic "risk factor" for ectopic pregnancy. Actually, all but the progesterone containing IUDs are relatively protective against ectopic pregnancy while the IUD is in place. That is, the number of ectopic pregnancies in women using an IUD for contraception is about one half that of women using no contraception. However, of IUD pregnancies there is a greater chance of an ectopic location (3-4%) since the number of intrauterine pregnancies with an IUD in place is markedly reduced. Additionally, IUDs can be associated with infections of the uterine cavity and fallopian tubes (especially just after insertion) which can independently increase the chance for an ectopic pregnancy. The Population Council's Center for Biomedical Research reviewed the association between IUDs and ectopic pregnancy and found that progestin only IUDs are the only nonprotective IUDs (in terms of ectopic pregnancy) when compared to women without contraception. The Progestasert IUD releases about 65 mcg of progesterone per day and large studies report a greater than 2 fold increase in ectopic pregnancy rates over women not using contraception. The reason for this increase is not clear. A theory is that somehow the progesterone enhances tubal implantation.
- a history of destruction of the uterine cavity or lining. If the woman has a history of uterine synechiae (scar tissue) from previous surgery (say, endometrial ablation for dysfunctional bleeding in a woman with no fertility interest) or if implantation is limited due to the presence of multiple submucosal fibroid tumors then a larger percentage of the pregnancies that are achieved will occur in a space other than the uterine cavity. Similar to the situation with IUDs, the total ectopic pregnancy rate may not be increased but when a pregnancy does occur the reduced likelihood of an intrauterine pregnancy increases the relative percentage of ectopic pregnancies.
- a history of DES exposure in utero. The mechanism for this association is not clear. There often are uterine cavity defects that may limit intrauterine implantation. Also, tubal defects exist that may increase the chance for a tubal ectopic pregnancy.
- a history of non-infectious pelvic inflammation (endometriosis, foreign body). Inflammation of the delicate tubal structures can result in adhesion formation (scar tissue), which will then increase the risk of an ectopic pregnancy. This inflammation may be due to endometriosis or the presence of a foreign body, either of which are strongly associated with scar tissue formation.
- Salpingitis Isthmica Nodosa. These uncommon diverticulae in the proximal (isthmic) portion of the fallopian tube may enhance tubal implantation. The cause of SIN is not known but most think it is related to chronic inflammation or infection.