The expected frequency of outcome measures varies
for different cardiovascular conditions in women in
Scotland, from 0.5% for electrocardiographic evidence
of myocardial infarction to over 8% for angina defined
by Rose questionnaire criteria. The frequency of
hypertension varies depending on the definition used.
One study of women aged 40-59 years in Scotland
identified 7% with a diastolic pressure greater than 100
mm Hg. For an outcome present in 5% of the control
group, a sample size of 932 subjects per group would
detect a doubling of risk, with 80% power at the 5%
level of significance. On this basis, we included all
women with pre-eclampsia or eclampsia (likely to be
the group with fewest potential members) in the
cohort and randomly sampled control and gestational
hypertension groups (matched for age and year of
delivery) of the same size as this group.