Final answer:
The most dangerous side effect of a fallopian ectopic pregnancy is a tubal rupture, potentially leading to severe internal bleeding and life-threatening conditions such as sepsis.
Step-by-step explanation:
The most dangerous complication of a fallopian ectopic pregnancy is a rupture of the uterine tube. This serious condition can lead to significant internal bleeding, which, if not treated promptly, can become life-threatening. Ectopic pregnancies occur when the embryo implants outside the uterus, commonly within the fallopian tubes due to scar tissue resulting from infections such as gonorrhea or chlamydia, which can lead to pelvic inflammatory disease (PID). If the tube ruptures, emergency surgical intervention is essential to repair the damage and prevent sepsis, a severe infection that can spread throughout the body.