Pre-eclampsia is the condition that typically occurs after 20 weeks of pregnancy. It is a combination of, raised blood pressure (hypertension), protein in your urine (proteinuria), plus or minus other signs like poor baby growth
That exact cause of pre-eclampsia is not understood. Often there are no symptoms and it may be picked up at your routine antenatal appointments when you have your blood pressure checked and urine tested. This is why your blood pressure & urine are monitored during appointments.