Ectopic pregnancy occurs when a fertilized egg implants in tissue outside the uterus. Left untreated, the condition can lead to serious complications, including hemorrhage and death.

Normally, after an egg is released by an ovary, it travels through the fallopian tube (narrow tubes that link the ovaries and the uterus) to the uterus (womb). If the egg joins with sperm in the fallopian tube, pregnancy begins. After being fertilized by the sperm, the fertilized egg, known as an embryo, travels further through the fallopian tube until it reaches the uterus three to four days later. Once in the uterus, the embryo implants in the lining of the uterus, where it begins to develop and grow.

In some women, however, the fallopian tube may be blocked or damaged. This can prevent the embryo from reaching the uterus. Instead, the fertilized egg may implant in the lining of the fallopian tube (tubal pregnancy). According to the American Society for Reproductive Medicine (ASRM), this is the most common form of ectopic pregnancy, accounting for approximately 95 percent of all cases. Although it occurs rarely, ectopic pregnancy may also develop in a woman’s ovary (ovarian pregnancy), cervix (cervical pregnancy), abdomen (abdominal pregnancy) or the narrow part where the fallopian tube and the uterus join (interstitial pregnancy).

In general, embryos that implant themselves outside the uterus are unable to survive. The uterus is the only organ that can safely and successfully support a pregnancy. As a result, the organs carrying ectopic pregnancies often rupture when the pregnancy outgrows the site of implantation. This serious condition can result in severe bleeding and lead to shock. For this reason, ectopic pregnancies can never continue to term. Currently, physicians are unable to remove the embryo and transplant it into the uterus to grow normally.

In some cases, the embryo is expelled by the fallopian tube at an early stage before rupture occurs. Known as a tubal abortion, this process may result in the pregnancy tissue deteriorating. In some women, the expelled tissue may reimplant in the ovary or abdomen. In other cases, the ectopic pregnancy may resolve on its own. However, the incidence of such “spontaneous resolution” is unknown.

In rare cases, an ectopic pregnancy can occur in a multiple pregnancy. In some twin pregnancies, one embryo may implant in the uterus while the other embryo implants in another location. Known as a heterotopic pregnancy, this condition occurs more often in women undergoing certain infertility treatments, such as in vitro fertilization or GIFT.

The incidence of ectopic pregnancy is rising. According to the National Institutes of Health (NIH), the rate increased four-fold between 1970 and 1992. The ASRM estimates that ectopic pregnancies account for 1 to 2 percent of all pregnancies.

Ectopic pregnancy is rarely fatal. According to the NIH, the maternal death rate from ectopic pregnancy in the United States is less than 0.1 percent but ectopic pregnancy can be a physically and emotionally traumatic experience. As a result, women may benefit from receiving psychological treatment from counseling and support groups.