Figure 1.

Diagnosis of hypertension in pregnancy: the timeline and trajectory of blood pressure elevations (“the 50% rule”)

The definition of hypertension in pregnancy required sustained hypertension, defined as blood pressure elevations in greater than 50% of readings, starting with the first blood pressure >140 mm Hg systolic, and/or >90 mm Hg diastolic (“the 50% rule”) (Figure 1A and Figure 1B-pregnancy 2). Pregnancy 1 in panel B illustrates why sustained elevations in blood pressure (BP) are important to confirm the diagnosis of gestational hypertension. A patient presents for a prenatal visit at 36 weeks, with a blood pressure of 142/76 mm Hg after rushing from the parking lot to her appointment. The measurement is repeated, giving a value of 134/68. All prior BPs were normal. She presents to clinic at 40 weeks complaining of painful contractions, with a blood pressure of 136/92 mm Hg. Her cervix is dilated to 6 cm and she is transferred to Labor and Delivery. Subsequent blood pressures are all normal and her urine and blood are negative for any abnormalities. She has one BP of 144/72 mm Hg just prior to epidural administration. The remaining blood pressures recorded during delivery and post-partum are all < 140/90 mm Hg. Diagnostic criteria that require only two BP elevations > 4 hours apart may categorize this woman as having gestational hypertension, but the majority of clinicians would not agree with this diagnosis.