Chronic hypertension
Chronic hypertension is defined as hypertension preceding
pregnancy. Blood pressure falls in the first and second trimesters.
Therefore women with high blood pressure before the 20th week
of pregnancy are assumed to have pre-existing or essential hypertension.
As many women of reproductive age present for
blood pressure measurement for the first time when pregnant,
chronic hypertension is often revealed in the first half of pregnancy.
Approximately 90e95% of cases of chronic hypertension
are considered to be essential. Secondary causes which account
for approximately 5e10% are listed in Table 2.