Since the systolic and diastolic blood pressures are measuring different phenomenon in your body, the diagnostic criteria for PE is if EITHER
the systolic is 140 or greater OR
the diastolic is 90 or greater. Because the systolic and diastolic BP are inter-related, most times the two numbers will increase together so that most hypertension has both numbers at or greater than 140/90.
I don't know for sure about the increase in chronic hypertension. I think that the treatment thresholds (ie. taking BP meds) is different for chronics vs non-chronics, but I don't think the diagnostic criteria is different. PE superimposed on chronic hypertension is a tricky, tricky condition.
A rise in BP of 30/15 is actually more important for a woman starting with a LOW BP (not a chronic). Prior to 2000, PE was diagnosed in anyone with a rise in BP of 30/15 from their individual baseline (as long as they also met the proteinuria criteria and/or had significant edema or swelling). But that diagnostic criteria is now outdated. See the "Woking Group Report on High Blood Pressure in Pregnancy" (http://www.preeclampsia.org/images/pdf/ ... rchive.pdf
). Instead, the official diagnostic criteria is that BP has to be 140/90 (either number) or greater. However, the physicians that made the newer recommendations for diagnostic criteria cautioned that any women with a rise of 30/15 should be closely monitored for any additional indications of PE.
Diana, happily married since 2007.
Miscarriage at 10 weeks (June 2009).
DD at 30+0 weeks weighing 2lbs 9oz (October 2010) due to PE and IUGR. Today, a happy and healthy toddler.