Hypertensive disorder during pregnancy includes pre-existing hypertensive disorders, hypertension arising in pregnancy and associated disorders such as eclampsia and preeclampsia.

Hypertension in pregnancy is defined as:

1. Systolic blood pressure greater than or equal to 140 mmHg and/or

2. Diastolic blood pressure greater than or equal to 90 mmHg.

Measurements should be confirmed by repeated readings over several hours. Elevations of both systolic and diastolic blood pressures have been associated with adverse fetal outcome and therefore both are important.

Disorders associated with hypertension such as eclampsia and preeclampsia are further characterised by symptoms such as proteinuria, oedema or high body temperature.

There are several reasons to support the blood pressure readings defined above as diagnostic of hypertension in pregnancy:

• perinatal mortality rises with diastolic blood pressures above 90 mmHg
• readings above this level were beyond two standard deviations of mean blood pressure in a New Zealand cohort of normal pregnant women
• the chosen levels are consistent with international guidelines and correspond with the current diagnosis of hypertension outside of pregnancy.

This definition of hypertensive disorder in pregnancy from the Society of Obstetric Medicine in Australia and New Zealand (SOMANZ) aligns with the definition of the International Society for the Study of Hypertension in Pregnancy (ISSHP).