What causes a woman to become pregnant in her tubes?

Normally, a fertilized egg travels through the Fallopian
tube to the uterus where it implants in the uterine lining, develops and grows into the
fetus. However, in approximately 2% of cases, an ectopic pregnancy occurs. This refers
to the fertilized egg developing someplace other than the uterus, in most cases, it is
in the Fallopian tube, that is why this is called a tubal pregnancy. Since this area is
small and doesn't have the amount of tissue to support the developing embryo, as the
embryo grows it will cause the organ its in to burst, which can harm the mother. These
pregnancies won't develop full term and the mother is at risk. Reasons why this can
occur are many. For example, if someone has scarring in the tubes due to Pelvic
Imflammatory Disease, which can be a result of syphillis or gonorrhea, causes
inflammation in the tubes. The fertilized egg can't pass through the tube to the uterus
and begins its development in the tube. Other reasons include, if the mother was exposed
to DES before she was born, she is at higher risk for a tubal pregnancy. If a woman had
prior fertility treatments or surgery in the Pelvic area, these can increase her risk of
ectopic pregnancy.  Smoking and endometriosis are all risk factors for the mother.
Symptoms include, vaginal bleeding and sharp pain in the abdominal
region.