Having your tubes tied, also known as having a tubal ligation, is generally accepted as an effective form of birth control. During the procedure, the fallopian tubes are cut and separated. When performed correctly, this procedure is 99.9% effective at preventing a pregnancy.
Unfortunately, some women are part of the lucky .01% that get pregnant after having a tubal ligation. This occurs when the tubes grow back together again during the recovery process. This means that the egg and sperm have the opportunity to connect. Additionally, these pregnancies tend to be ectopic, meaning that the fertilized egg implants inside the fallopian tube instead of the uterus. These pregnancies are generally not viable.
Always check with your doctor regarding questions on your health for you or you baby.