High Blood Pressure and Pregnancy

How to Tell the Difference between Chronic Hypertension and PIH

One of the perplexing challenges for an obstetrician is discerning the difference between chronic hypertension and PIH when a patient presents with hypertension.

It helps to know just what normal blood pressure is. I always tell my patients that the best blood pressure is the lowest pressure you can have without passing out. In the non-pregnant state, we doctors like to see the blood pressures under 140/90. In pregnancy, blood pressures tend to be a little lower, anywhere from 90/50s to 110/70s.

A patient with chronic hypertension will generally begin her pregnancy with hypertension or come to me on anti-hypertensive medication from another doctor (a sure tip-off!). Unless there are major changes during the pregnancy (like piling on PIH, too), the blood pressure of a hypertensive patient will usually behave itself, rising only slightly over the course of the pregnancy.

On the other hand, a patient that develops PIH will begin her pregnancy with a normal blood pressure, but it will typically rise sometime in the third trimester. In severe cases, it will rise earlier in the pregnancy. The actual criteria that need to be met before suspecting PIH is a rise in the systolic number (the top number) of 30 and/or a rise of the diastolic number (the bottom number) of 15. For example, a blood pressure that usually runs about 100/60 and then presents as 140/84 would warrant suspicion. The blood pressure changes are only part of the classical tetrad of signs that are associated with the older referenced term, preeclampsia.

These four noteworthy signs and symptoms are:

• High blood pressure (as defined by the criteria above)
• Hyperproteinurea (spilling protein in the urine)
• Hyper-reflexia, or exaggerated deep-tendon reflexes (the knee-jerk, for instance)
• Edema (swelling), more suggestive of PIH if it occurs in the face rather than the ankles