In theUSA, ectopic pregnancies are reported. This allows
some tabulation of incidence rates and outcomers.
The Centers for Disease Control (CDC) examined ectopic pregnancies
occurring during the 17 year period between 1970 and 1987 and noted
- 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) is responsible
for a significant portion of the increased number of cases of ectopic
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 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
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.