Ectopic pregnancy is an ectopic pregnancy and bleeding from a ruptured ectopic pregnancy can cause a collection of fluid in the rectal fossa of the uterus, but a collection of fluid in the rectal fossa of the uterus does not necessarily mean an ectopic pregnancy.
If necessary, the doctor will perform a posterior vaginal fornix puncture and draw non-clotting blood in the rectal fossa of the uterus indicating an accumulation of blood in the abdominal cavity, which is considered a high probability of ectopic pregnancy.