Final answer:
Sharp, tearing pain with a stiff, boardlike abdomen in a pregnant patient likely indicates placental abruption, which is a serious obstetric emergency.
Step-by-step explanation:
Sharp, tearing pain and a stiff, boardlike abdomen without vaginal bleeding in a pregnant patient may indicate a placental abruption. This is a serious condition where the placental lining has separated from the uterus of the mother prior to delivery, which could be life-threatening for both mother and baby. Ectopic pregnancy is characterized by sharp pain usually accompanied by vaginal bleeding; appendicitis typically involves right lower quadrant abdominal pain, not stiff abdomen; and round ligament pain is usually a brief and often sharp pain that is most likely not characterized by a boardlike abdomen.