Maternal cardiovascular dynamics. VII. Intrapartum blood volume changes.

Blood volume was measured in 75 normal pregnant women at term and serially at 10 and 60 minutes and on Days 1 and 3 post partum in women delivered vaginally and on Days 1, 3, and 5 in women who underwent cesarean section. The mean blood volume at term was 5.95 L. and 83.3 c.c. per kilogram, an increase of 44 and 16%, respectively, over nonpregnant values. The increment appeared to be related to lean body mass and the weight of the neonate alone and to the combined weights of the neonate and placenta, but the wide range of values precluded statistical significance. The blood volume loss at 60 minutes post partum was 610 c.c. (10.2%) for patients delivered vaginally and 1,030 c.c. (17.4%) for those delivered by cesarean section. The blood volume showed a steady decline to Day 3 post partum in the vaginal delivery group, whereas it remained fairly stable from 60 minutes to Day 5 post partum in the surgically delivered group. Remarkably, the volume had declined by the amount, 16.2%, in both groups on the third postpartum day. On the other hand, the hematocrit showed a rise of 5.2% in the former group and a decline of 5.8% in the latter. A remarkable tolerance for blood loss at delivery was demonstrated. A more realistic definition of postpartum hemorrhage is strongly recommended.