Blood pressure, plasma osmolarity and oedema in pregnancy

Relations of mean arterial pressure to age, parity, plasma, osmolarity, sodium and albumin were examined in normal non-pregnant, normal pregnant and pre-eclamptic Nigerian women. Mean arterial pressure showed a positive correlation with age in non-pregnant subjects, but not in normal pregnant or pre-eclamptic women. There was no significant correlation of mean arterial pressure with parity, plasma sodium or albumin in any of the three groups. A weak positive correlation was found between mean arterial pressure and plasma osmolarity in non-pregnant women and, although this was absent in normal pregnancy, it reappeared as a significant negative correlation in pre-eclampsia. These observations were considered, with special reference to osmotic aspects of the changes involved, and biophysical aspects of oedema are discussed. It is suggested that the osmotic properties of interstitial fluid albumin play a key role in the development of both physiological and pathological oedema in pregnancy.