An ectopic pregnancy is a complication of pregnancy in which the fertilized ovum is implanted in any tissue other than the uterine wall. Most ectopic pregnancies occur in the Fallopian tube (so-called tubal pregnancies), but implantation can also occur in the cervix, ovaries, and abdomen. The fetus produces enzymes that allow it to implant in varied types of tissues, and thus an embryo implanted elsewhere than the uterus can cause great tissue damage in its efforts to reach a sufficient supply of blood.

Overview

In a typical ectopic pregnancy, the embryo does not reach the uterus, but instead adheres to the lining of the Fallopian tube. The implanted embryo burrows actively into the tubal lining. Most commonly this invades vessels and will cause bleeding. This intratubal bleeding (hematosalpinx) expels the implantation out of the tubal end as a tubal abortion. Some women thinking they are having a miscarriage are actually having a tubal abortion. There is no inflammation of the tube in ectopic pregnancy. The pain is caused by prostaglandins released at the implantation site, and by free blood in the peritoneal cavity, which is a local irritant. Sometimes the bleeding might be heavy enough to threaten the health or life of the woman. Usually this degree of bleeding is due to delay in diagnosis, but sometimes, especially if the implantation is in the proximal tube (just before it enters the uterus), it may invade into the nearby Sampson artery, causing heavy bleeding earlier than usual.

If left untreated, about half of ectopic pregnancies will resolve without treatment. These are the tubal abortions. The advent of methotrexate treatment for ectopic pregnancy has reduced the need for surgery; however, surgical intervention is still required in cases where the Fallopian tube has ruptured or is in danger of doing so. This intervention may be laparoscopic or through a larger incision, known as a laparotomy.

Causes

The causes of ectopic pregnancy are unknown. After fertilization of the oocyte in the peritoneal cavity, the egg takes about 6 days to migrate down the tube to the uterine cavity at which time it implants. Wherever the embryo finds itself at that time, it will begin to implant.

There are some speculative specific causes or associations. Smoking, advanced maternal age and prior tubal damage of any origin are well known risk factors for ectopic pregnancyFact: date=August 2007.

Cilial damage and tube occlusion

Hair-like cilia located on the internal surface of the Fallopian tubes carry the fertilized egg to the uterus. Damage to the cilia or blockage of the Fallopian tubes is likely to lead to an ectopic pregnancy. Women with pelvic inflammatory disease (PID) have a high occurrence of ectopic pregnancy. This results from the build-up of scar tissue in the Fallopian tubes, causing damage to cilia. If however both tubes were occluded by PID, pregnancy would not occur and this would be protective against ectopic pregnancy. Tubal surgery for damaged tubes might remove this protection and increase the risk of ectopic pregnancy. Tubal ligation can predispose to ectopic pregnancy. Seventy percent of pregnancies after tubal cautery are ectopic, while 70% of pregnancies after tubal clips are intrauterine. Reversal of tubal sterilization (Tubal reversal) carries a risk for ectopic pregnancy. This is higher if more destructive methods of tubal ligation (tubal cautery, partial removal of the tubes) have been used than less destructive methods (tubal clipping). A history of ectopic pregnancy increases the risk of future occurrences to about 10%. This risk is not reduced by removing the affected tube, even if the other tube appears normal. The best method for diagnosing this is to do an early ultrasound.