Figure 1: Relative changes in renal hemodynamics during normal human pregnancy. Dramatic changes occur in systemic hemodynamics during physiologic pregnancy. In uncomplicated pregnancy, mean arterial pressure drops, reaching its nadir between the 16th and 20th weeks of gestation. After the 20th week, mean arterial blood pressure slowly returns to close to pre-pregnancy levels at about 40-week gestation. Changes in systemic blood pressure are paralleled by a change in cardiac output which increases dramatically. The apex is reached between the 16th and 20th weeks of gestation. Plasma volume increases substantially as well but lags behinds the increased cardiac output. MAP: mean arterial pressure. CO: cardiac output.