An ectopic pregnancy is an abnormal pregnancy that occurs outside the womb (uterus). The baby (fetus) cannot survive, and often does not develop at all in this type of pregnancy.

An ectopic pregnancy occurs when a pregnancy starts outside the womb (uterus). The most common site for an ectopic pregnancy is within one of the tubes through which the egg passes from the ovary to the uterus (fallopian tube). However, in rare cases, ectopic pregnancies can occur in the ovary, stomach area, or cervix.

An ectopic pregnancy is often caused by a condition that blocks or slows the movement of a fertilized egg through the fallopian tube to the uterus. This may be caused by a physical blockage in the tube by hormonal factors and by other factors, such as smoking.

Most cases of scarring are caused by:

• Past ectopic pregnancy
• Past infection in the fallopian tubes
• Surgery of the fallopian tubes

Up to 50% of women who have ectopic pregnancies have had swelling (inflammation) of the fallopian tubes (salpingitis) or pelvic inflammatory disease (PID).

Some ectopic pregnancies can be due to:

• Birth defects of the fallopian tubes
• Complications of a ruptured appendix
• Endometriosis
• Scarring caused by previous pelvic surgery

The following may also increase the risk of ectopic pregnancy:

• Age over 35
• Having had many sexual partners
• In vitro fertilization

In a few cases, the cause is unknown.

Sometimes, a woman will become pregnant after having her tubes tied (tubal sterilization). Ectopic pregnancies are more likely to occur 2 or more years after the procedure, rather than right after it. In the first year after sterilization, only about 6% of pregnancies will be ectopic, but most pregnancies that occur 2 - 3 years after tubal sterilization will be ectopic.

Ectopic pregnancy is also more likely in women who have:

• Had surgery to reverse tubal sterilization in order to become pregnant
• Had an intrauterine device (IUD) and became pregnant (very unlikely when IUDs are in place)

Ectopic pregnancies occur in 1 in every 40 to 1 in every 100 pregnancies.