I'd say elevated blood pressure would probably be of the most concern... though of course a pregnant woman would probably show other signs before elevated blood pressure becomes a concern. Elevated blood pressure is one of the main symptoms of preeclampsia, which is a potentially fatal pregnancy complication. However, blood pressure doesn't typically elevate until the last trimester. A more reliable early detection of preeclampsia is protein in the urine, which to my knowledge can show up much earlier than elevated blood pressure and would make the condition much easier to treat.