If you have a positive pregnancy (positive hCG) test, but subsequent tests do not show a normal rise in the hCG level and an ultrasound shows no fetus, you may have an ectopic pregnancy.
In a normal pregnancy, the fetus attaches to the wall of the uterus and begins growing inside the womb; however, sometimes the fetus and implants in an abnormal location such as in one of the Fallopian tubes instead of in the uterus. This is called an ectopic pregnancy. The Fallopian tube cannot carry a pregnancy and will likely burst, causing an internal hemorrhage. If this happens, the situation becomes a medical emergency and may require urgent surgery.
If you have had a positive pregnancy test and feel sudden and severe abdominal pain, make sure you go to the emergency room and inform the medical staff that you have received fertility treatment and that you are pregnant. Since you are monitored closely while undergoing fertility treatment, most ectopic pregnancies are diagnosed early and are usually not an acute emergency.