Aguree S, et al. - As plasma volume expansion is an important physiologic change across gestation, researchers investigated the pattern of plasma volume expansion across healthy pregnancies from longitudinal studies. They identified 10 observational studies with a total of 347 pregnancies for inclusion in this work. The analysis revealed that in healthy pregnancies, expansion of plasma volume initiates in the first trimester. The steepest rate of increase is observed in the second trimester, and it peaks late in the third trimester. As 7 out of 10 included studies were conducted over 30 years ago, the patterns observed in these studies may not reflect the current population. The changes in BMI over the last several decades may partly explain this. These findings suggest the necessity for undertaking additional longitudinal studies to better characterize the range of normal plasma volume expansion across maternal characteristics.