Final answer:
In a tubal pregnancy, the embryo implants within the uterine tube rather than the uterus, typically due to scar tissue from an infection blocking the passage.
Step-by-step explanation:
In a tubal pregnancy, the embryo implants itself within the uterine tube instead of completing its journey to the uterus. This type of ectopic pregnancy is often due to scar tissue within the uterine tube, which can arise from a sexually transmitted infection.
This scar tissue may block the embryo's progress or snag it, preventing it from reaching the uterus. Approximately one half of tubal pregnancies resolve spontaneously with the embryo being expelled due to bleeding and muscle contractions. The remaining cases require medical intervention, such as the administration of the cytotoxic drug methotrexate, which stops the embryo's development, or surgical intervention if the uterine tube ruptures.
Some resolve spontaneously, while others require medical or surgical intervention.