The symptoms of pregnancy with Mirena are the same as regular pregnancy symptoms. According to the Woman's Clinic of Pennsylvania, a tubal pregnancy is a potential side effect of using Mirena, and it causes abdominal pain on one side. The clinic warns that pregnancy with Mirena in place is a medical emergency.
According to the Mirena product website, one risk having the Mirena intrauterine device, or IUD, in place is a tubal pregnancy. According to the Mayo Clinic, tubal pregnancy is an ectopic pregnancy occurring in one of the Fallopian tubes. An ectopic pregnancy is a pregnancy in which the embryo implants in a location other than the uterine walls. Symptoms of a tubal pregnancy do not start until the embryo grows so much that it stretches the tube. A tube with an embryo in it is at risk of rupture, so immediate treatment is important. The May Clinic indicates that the warning signs of a tubal pregnancy include severe abdominal pain on one side, vaginal bleeding, feeling lightheaded and fainting.
According to the Mirena product website, a normal pregnancy with an IUD in place is also risky. Infection, including sepsis, is a major risk as long as the IUD is in place. If the IUD is removed during pregnancy, there is a risk of miscarriage, but the risk of infection returns to zero after removal of the device. Other complications of pregnancy associated with using an IUD include preterm birth, miscarriage and death.
According to the Mirena product website, the side effects of the Mirena IUD include vaginal discharge, tender breasts, absent or lighter periods, migraines, acne and nausea, which are all common pregnancy symptoms. Since less than eight in 1,000 women become pregnant while the Mirena IUD is in place, it is unlikely that these symptoms indicate pregnancy. However, due to the risks, anyone using the Mirena IUD who has pregnancy symptoms should seek medical care as soon as possible.