Emerging understanding and measurement of plasma volume expansion in pregnancy.

Plasma volume expansion is an important component of a successful pregnancy. The failure of maternal plasma volume expansion has been implicated in adverse obstetric outcomes such as pre-eclampsia, fetal growth restriction, and preterm birth. Altered iron homeostasis and elevated maternal hemoglobin concentrations have also been associated with adverse pregnancy outcomes; limited data have suggested that these effects may be mediated by inadequate plasma volume expansion. In addition, it has been noted that pregnant, obese women, compared with lean subjects, have decreased plasma volume expansion along with impaired iron homeostasis and increased inflammation. Current estimates of plasma volume expansion are outdated and do not necessarily reflect contemporary obstetric populations. Moreover, the validation of clinically applicable methods of plasma volume determination as well as enhanced methodologies should be a priority. Further study is needed to characterize diminished plasma volume expansion during pregnancy and to understand the potential role of impaired iron homeostasis and inflammation in adverse obstetric outcomes, especially in obese women.