The impact of mean arterial pressure in the middle trimester upon the outcome of pregnancy.

Data on the outcome of pregnancy are based upon a prospective study of 14,833 single births to women whose blood pressures during the fifth and sixth months of gestation were recorded. With each 5 mm, Hg rise in the mean arterial pressure (MAP) there is a progressive increase in the perinatal mortality rate. At each MAP level, the stillbirth rates and neonatal mortality rates are higher in blacks than in whites. When middle-trimester MAP is 90 mm. Hg or more, there is a significant increase in (1) the stillbirth rate, (2) the frequency of proteinuria, hypertension, and diagnosed pre-eclampsia in the third trimester, and (3) the frequency of intrauterine fetal growth retardation. We believe that all of these events are due to an impaired uteroplacental circulation, with which elevated blood pressures are associated. Women who have an average MAP of 90 or more during the fifth and sixth months should be considered in a high-risk category.