First trimester maternal blood rheology and pregnancy induced hypertension

Blood rheology during normal pregnancy

INTRODUCTION

Recent studies have shown increased RBC aggregation and no difference in plasma viscosity in the presence of markedly lower hematocrit in women at term compared to non-pregnant women. Little is known about the outcome of blood rheological parameters and red blood cell (RBC) deformability particularly in the course of normal pregnancy.

METHODS

During a 36 months interval 1.913 blood samples were randomly collected from a total of 945 pregnant women in the course of their pregnancy (n = 1.259) and during puerperium (upto 1 week; n = 654). Next to the blood count, hemorheological parameters including red blood cell (RBC) -aggregation (stasis E0; low shear E1), -deformability (low, moderate and high shear conditions) and plasma viscosity (pv) were assessed. Plasma viscosity (pv) was examined using KSPV 1 Fresenius, RBC aggregation (stasis: E0 and low shear: E1) using MA1-Aggregometer; Myrenne and RBC deformability (def) was determined by Rheodyn SSD Diffractometer, Myrenne, Roetgen, Germany were tested. In some of these women laboratory results prior to pregnancy (n = 145) were available which were compared with those during pregnancy.

RESULTS

Mean maternal pv remained unchanged within each trimester and compared to the values before pregnancy and during early puerperium (Range of means: 1.18-1.20 mPa S). In contrast, RBC agg (E0 and E1) was markedly higher in the 2nd (21.8 ± 7.0 and 28.9 ± 9.4; p < 0.001) and 3rd trimester (18.74 ± 8.4 and 28.2 ± 9.4; p < 0.01) compared to the values before pregnancy (16.4 ± 6.4 and 20 ± 7.5) and during 1st trimester (17.49 ± 6.5 and 22.4 ± 7.4). There was a stat. significant temporary reduction in RBC def. under all shear rate conditions during 2nd trimester compared to the values before pregnancy which remained significantly lower during 3rd trimester only under high shear rates.An increase RBC agg was stat. significantly inversely correlated with reduced RBC def being most pronounced under low shear rate conditions. While RBC rigidity was stat. significantly correlated with higher hematocrit values there was only a weak correlation between RBC agg and haematocrit (E0: r = -0.084; p = 0.03; E1: r = -0.06; p = 0.1). Pv was not correlated with haematocrit or RBC def but stat. significantly correlated with RBC agg.

CONCLUSIONS

Blood rheological changes manifest during 1st trimester, and fairly remain unchanged during 2nd trimester until term. Physiologic hemodilution and increasing hypercoagulability is accompanied by high RBC -aggregation and - rigidity during 2nd trimester while plasma viscosity remains nearly unaffected throughout normal pregnancy.

Computational patient-specific models based on 3-D ultrasound data to quantify uterine arterial flow during pregnancy

Information on uterine blood flow rate during pregnancy would widely improve our knowledge on feto-placental patho-physiology. Ultrasonographic flow rate evaluation requires the knowledge of the spatial velocity profiles throughout the investigated vessel; these data may be obtained from hemodynamic simulations with accurate computational models. Recently, computational models of superficial vessels have been created using 3-D ultrasound data; unfortunately, common reconstruction methods are unsuitable for the uterine arteries due to the low quality achievable of imaged deep vessels. In this paper a simplified spline-based technique was applied to create computational models for patient-specific simulations of uterine arterial heamodynamics. Moreover, a novel method to quantify the uterine flow rates was developed based on echo-Doppler measurements and computational data. Preliminary results obtained for four patients indicated a quite narrow range for the blood flow rate through the main uterine artery with large variability in the flow split between corporal and cervical branches. Furthermore, parabolic-like velocity profiles were obtained in the branching region of the different patients, suggesting a clinical use of averaged, not patient-specific, spatial velocity distribution coefficients for the blood flow rate calculation. The developed reconstruction method based on 3-D ultrasound imaging is efficient for creating realistic custom models of the uterine arteries. The results of the fluid dynamic simulations allowed us to quantify the uterine arterial flow and its repartition in normal pregnancies.