Construction and characterisation of a longitudinal clinical blood pressure database for epidemiological studies of hypertension in pregnancy.

Blood pressure measurement plays a central role in the screening and management of hypertension during pregnancy. Although descriptions of changes in blood pressure patterns of normotensive and hypertensive pregnancies are plentiful, relatively little is known about how modifiable environmental and lifestyle characteristics, including maternal diet and physical activity, influence blood pressure levels in pregnancy. In this paper we provide a detailed description of the first 2000 subjects enrolled in the Omega Prospective Cohort Study. Our intention is to characterise the cohort and to establish a rigorous data framework that will form the basis for future analyses of the association between blood pressure patterns in pregnancy and modifiable risk factors. We describe the construction of a representative longitudinal blood pressure analysis database drawn from routinely collected measurements. In doing this, we explore possible over- and under-representation of patients and evaluate ways of modifying the database to address areas of possible bias. In addition, we consider questions of data quality which are specific to blood pressure measurements. In an accompanying paper, we use this database to explore the influence of maternal pre-pregnancy adiposity on blood pressure levels across gestation.