Ectopic pregnancy can cause the burst of fallopian tube. If previous ectopic pregnancy occured then again onset of this type of pregnancy may lead to life threatening bleeding. Having the abdominal surgery before may also proved as a risk.
LD50 is a measure of toxicity in animals. A chemical with a smaller LD50 is more toxic and in this question, Shiga toxin has a lower LD50, thus it is more lethal.
