Blood volume determination in obese and normal-weight gravidas: the hydroxyethyl starch method

Abstract

Objective The impact of obesity on maternal blood volume in pregnancy has not been reported. We compared the blood volumes of obese and normal weight gravidas using a validated Hydroxyethyl Starch (HES) dilution technique for blood volume estimation. Study Design Blood volumes were estimated in 30 normal weight (pregravid body mass index; BMI < 25 kg/ m2) and 30 obese (pregravid BMI > 35 kg/m2) gravidas after 34 weeks gestation using a modified HES dilution technique. Blood samples obtained before and 10 minutes after HES injection were analyzed for plasma glucose concentrations after acid hydrolysis of HES. Blood volume was calculated from the difference between glucose concentrations measured in hydrolyzed plasma. Results Obese gravidas had higher pregravid and visit BMI (mean [Std Dev]): pregravid (41[4] vs 22[2] kg/m2, p=0.001); visit BMI (42[4] vs 27[2] kg/m2, p=0.001), but lower weight gain (5[7] vs. 12[4] kg, p=0.001) than normal weight women. Obese gravidas had similar estimated total blood volume to normal weight women (8103 ± 2452 vs. 6944 ± 2830 mL, p = 0.1), but lower blood volume per kilogram weight (73 ± 22 vs. 95 ± 30 mL/kg, p = 0.007). Conclusion Obese gravidas have similar circulating blood volume, but lower blood volume per kilogram body weight, than normal weight gravidas near term.

Emerging understanding and measurement of plasma volume expansion in pregnancy

“…However, because fat mass is relatively underperfused compared with lean mass, the relation is curvilinear rather than linear, which results in estimates of 29-45 mL/kg in obese nonpregnant women (Table 1) (36,38,40). Plasma volume expansion in obese pregnant women remains understudied, although our recent publication suggests that it follows a similar trend to that in obese nonpregnant women (39). Investigation of abnormalities in plasma volume expansion in various disease states of pregnancy has also been limited, although some studies that were performed in pre-eclamptic patients have provided the basis for our understanding of this condition as one of volume contraction with decreased plasma volume estimates in pre-eclamptic women compared with in healthy and hypertensive controls (41).…”

Normal Values of Hemoglobin Mass and Blood Volume in Young, Active Women and Men

“…Often, the hematological parameters are usually normalized to body weight (BW) or body surface area (BSA) [5,6,24,30,34,62,64,75]. Therefore, obese individuals show lower BV to body weight after weight loss or in comparison to non-obese individuals [3,27,40,72]. The BSA has no physiological relationship to BV [18,44].…”

Approaches for optimising intravenous iron dosing in pregnancy: a retrospective cohort study

“…Given that body composition varies as a function of total bodyweight, optimising dosing in this population requires the identification of size descriptors, such as adjusted bodyweight, that share a quantitative relationship with changes in pharmacokinetics and associated pharmacological activity. When it comes to intravenous iron, it has been previously demonstrated that pregnant women who are overweight or obese have a greater total blood volume, which in turn would require a greater amount of iron to increase haemoglobin concentration relative to an individual of ideal bodyweight and a lower total blood volume.…”