About one in one hundred pregnancies, mostly in older women, is ectopic, meaning the fertilized egg does not correctly implant in the uterine lining. Generally, it instead rests in the fallopian tubes, which lead from the ovaries to the uterus. This may be a result of damage or inflammation in the reproductive organs, but sometimes the cause is simply unknown.
When this happens, the fetus is unable to properly develop and is not viable. However, left alone, the fetal tissue will develop for a certain amount of time before dying, possibly damaging the mother’s internal organs. This is why ectopic pregnancies often require medical or surgical intervention.
Ectopic pregnancies feel like normal ones at first. The initial indicators of pregnancy—such as missed periods and nausea—are the same whether the embryo implanted normally or not. However, ectopic pregnancy is soon after indicated, often, by unusual pelvic or abdominal pain, and doctors can usually diagnose it at around eight weeks. There may also be some vaginal bleeding, which resembles period bleeding despite a positive pregnancy test. The fallopian tube may leak blood, which can cause the feeling of needing to go to the bathroom, or even shoulder pain.
Sometimes the fallopian tube ruptures, causing lightheadedness and shock; this is actually a medical emergency and you should call 911. By contrast, sometimes there are no symptoms at all, and the problem is not found until a prenatal doctor visit.
While it is possible to have a normal pregnancy after an ectopic pregnancy, each one does make subsequent ones more likely. This risk can be reduced by having the non-viable embryo removed sooner rather than later. Women over 35 are at high risk regardless of previous pregnancy history. Some fertility drugs can also raise the likelihood. On the other hand, while fertilization after surgical sterilization or while using an IUD is vanishingly rare, when it does happen there is a strong probability of ending up outside the uterus.
Smokers have a high risk of experiencing ectopic pregnancy, because cigarette smoke causes changes that make the fallopian tube environment resemble that of the uterus just enough to encourage implantation. Some medical conditions can increase the risk of ectopic pregnancy, such as endometriosis, pelvic inflammatory disease, or chlamydia.