Mean arterial pressure in the three trimesters of pregnancy: Effects of maternal characteristics and medical history

Abstract

Objective To define the contribution of maternal variables that influence the measured mean arterial pressure (MAP) in screening for pregnancy complications. Methods Maternal characteristics and medical history were recorded, and MAP was measured, in women with a singleton pregnancy attending for three routine hospital visits at 11+0 to 13+6weeks, 19+0 to 24+6weeks and 30+0 to 34+6weeks or 35+0 to 37+6weeks' gestation. For pregnancies delivering phenotypically normal live births or stillbirths at ≥24weeks' gestation, variables from maternal demographic characteristics and medical history that are important in the prediction of MAP were determined from linear mixed-effects multiple regression analysis. Results MAP was measured in 75841 cases in the first trimester, 30447 in the second trimester and 31673 in the third trimester. Significant independent contributions to MAP were provided by gestational age, maternal age, weight, height, Afro-Caribbean racial origin, cigarette smoking, family history of pre-eclampsia (PE), history of PE in the previous pregnancy, interpregnancy interval, chronic hypertension and diabetes mellitus. The effects of some variables were similar, and for others differed, in the three different trimesters. Random-effects multiple regression analysis was used to define the contribution of maternal variables that influence the measured MAP and express the values as multiples of the median (MoMs). The model was shown to provide an adequate fit of MoM values for all covariates, both in pregnancies that developed PE and in those without this complication. Conclusions A model was fitted to express the measured MAP as MoMs after adjustment for variables from maternal characteristics and medical history that affect this measurement.