How Much Does Plasma Volume Rise in Pregnancy?

Plasma volume starts expanding immediately in pregnancy and is increased by 50% by 28 weeks. One panelist says the rise is pretty linear, really accelerates in the second part of the second trimester, and then levels off. Asked how much of the mother's plasma expansion occurs in the first trimester, one panelist places the start at the very beginning and the total increase at 50% by 28 weeks.

A co-host calls a 50% increase in plasma volume by 28 weeks remarkable. A co-host asks whether the rise comes with a fifty percent increase in oxygen-carrying capacity, and whether hemoglobin concentration expands to compensate. One panelist says a relative anemia forms due to the expansion. The larger plasma volume leaves the mother's blood relatively dilute because hemoglobin concentration does not expand in step with it.