increased blood pressure and then protein in your urine. They will make you do a 24hr urine test, you basically put all urine in a jug over a 24 hr period and they will test that. I know last pregnancy i tested high every time I went to the dr but my 24 test came back normal. I just started making sure I had lots of water on the days I went to the dr's after that.
My doc also said watch for dizziness and seeing stars at unusual times. Also headaches that won't go away.
An increase in blood pressure, an increase of 30 for top or bottom number, and swelling are common signs. They test urine protein, there is also a blood test, at 30 weeks they have a lot of different things they do to protect you and baby. Don't worry, many women develop pre eclampsia and have healthy babies.
At my doctors they check for protein every single time