Objective: The aim of this study was to test the hypothesis that standardization of cardiac output in pregnancy by correcting for body surface area, and thus obtaining cardiac index, is justified.
Study design: Cardiac output was determined by thoracic electrical bioimpedance monitoring in 78 pregnant women; recordings were made at 1-month intervals from the first antenatal visit and a further two were made during the sixth and twelfth weeks after delivery. In a separate group of 10 pregnant women, cardiac output was determined by Doppler echocardiography at 5, 10, 14, 25, and 35 weeks and at 12 weeks post partum.
Results: Irrespective of gestational age, the correlation between cardiac output and body surface area was poor, by either thoracic electrical bioimpedance monitoring (r = 0.15 to 0.39) or Doppler echocardiography (r = 0.00 to 0.29). Furthermore, strict proportionality between cardiac output and body surface area was in general not the best way of describing the (poor) relation between these two.
Conclusion: Standardization of cardiac output in pregnancy by correcting for body surface area to compare cardiac performance between individuals and between groups of individuals is not justified.