In a normal pregnancy, fertilization takes place in the uterine tube and then the fertilized egg travels along the tube to the main cavity of the uterus, where it is implanted in the uterine lining. In an ectopic pregnancy, however, the ovum never completes the journey to the uterine cavity.

Instead, implantation occurs in the uterine tubes, abdomen, or even, in rare instances, in the ovarian follicle if fertilization takes place before the egg is released. Ectopic pregnancies are nearly impossible to carry to term and usually result in spontaneous abortion. The condition is relatively common, occurring about once in every 300 pregnancies.

The most frequent type of ectopic pregnancy is the tubal variety, which can be particularly dangerous to the mother if it involves implantation in the narrow portion of the tube near the uterus called the isthmus, rather than the larger, more expandable ampulla or infundibulum. This is because as the fertilized egg attempts to grow and divide, the isthmus attempts to stretch but is so narrow and inflexible that it soon ruptures, causing profuse internal hemorrhaging that can lead to death. Tubal rupture may also occur when the ovum is implanted in other regions of the uterine tube, but at a lower rate of incidence since the longer amount of time it takes to occur means that there is a better chance that the condition will be recognized before the tube becomes physically damaged.

Ectopic pregnancies can be difficult to diagnose and sometimes go completely unnoticed, especially when the fetus dies at a very early stage and is resorbed by the body. Cases are even known when fetal death occurred at a later time and instead of being resorbed or expelled, was carried for substantial amounts of time in a sort of mummified form without the appearance of any symptoms. In some instances, individuals may also experience what is known as a combined pregnancy, in which one pregnancy is the normal uterine variety and the other is an ectopic pregnancy. This unusual condition can make diagnosis even more problematic, but when recognized, can often be treated so that the uterine fetus survives and the abnormal pregnancy is ended. Signs of a more typical ectopic pregnancy frequently, but not invariably, involve missed periods, abdominal pain, recurrent irregular bleeding, and weakness. Also, oftentimes pregnancy tests will provide mixed results, and certain common symptoms of pregnancy, such as morning sickness, are absent. Rarely, the intense pain and hemorrhaging associated with rupture are the first indications that anything is wrong.

Specific causes of ectopic pregnancies are not generally known. Some medical professionals have suggested that many times the condition is a result of scarring, kinks, pockets or other irregularities in the lining of the uterine tubes caused by prior infection, but oftentimes no tubal abnormality can be found. Damage to the cilia lining the uterine tubes is another possible cause of ectopic pregnancy since the hair-like structures are important in the process of pushing the fertilized egg towards the uterus. Also, certain hormones or hormonal imbalances are theoretically capable of resulting in an abnormal implantation site for the ovum as well because they can slow the speed at which the mass travels along the uterine tube. This delay could allow the egg to mature to a level that signals it is ready for implantation before it actually reaches the cavity of the uterus.

Ruptured Ectopic Pregnancy at 20x Magnification - When conservative surgical means are utilized as a treatment, there is some risk of persistent ectopic pregnancy, which entails any remaining tissue from the original pregnancy resuming growth and expansion so that symptoms may recur and rupture is still a possibility for the patient.

Ruptured Ectopic Pregnancy at 40x Magnification - Most ectopic pregnancies that are diagnosed before the fetus dies on its own are ended through surgical means. Depending on the specific case and the concern for future fertility, surgery may involve small incisions and conservative measures or may be a more extensive process in which the affected tube is removed in part or in its entirety.

Ruptured Ectopic Pregnancy at 20x Magnification - Since the early 1990s, the drug methotrexate, which inhibits rapidly growing cells, has been used as an alternate treatment in cases of ectopic pregnancy that are recognized at an early stage. The chance of persistent ectopic pregnancy following the administration of this form of treatment, however, is comparable to that associated with conservative surgical measures.