Blood viscosity and haemostatic factors in late pregnancy, pre-eclampsia and fetal growth retardation

Effect of Intrapartum Maternal Hemoglobin on Mode of Delivery and Short-Term Neonatal Outcome: A Systematic Review

Importance

Maternal anemia in pregnancy is a common condition worldwide and is considered a risk factor for adverse neonatal and maternal outcome. Also high hemoglobin (Hb) levels are associated with adverse pregnancy outcomes. However, studies regarding the influence of intrapartum maternal Hb on mode of delivery and short-term neonatal outcome are limited and contradicting.

Objective

The aim of this study was to provide an overview of current evidence regarding associations between intrapartum maternal Hb levels and mode of delivery and short-term neonatal outcome. In addition, we propose directions for future research.

Evidence Acquisition

We systematically searched the electronic PubMed, EMBASE, and Cochrane databases for studies on maternal Hb levels and mode of delivery maternal and short-term neonatal outcome until January 2021. Eligible articles and their references were independently reviewed by 2 authors. Assessment was based on methodological quality and study results.

Results

We included 14 studies that evaluated the level of maternal pH in relation to clinical outcome, 6 studies on mode of delivery, 10 studies on Apgar score, 1 study on fetal distress, 2 studies on neonatal intensive care unit admission, 1 study on umbilical cord pH, and 5 studies on perinatal mortality.

Conclusions and Relevance

We found a trend toward an increased risk of cesarean delivery in anemic woman. Concerning the short-term neonatal outcomes, the evidence is conflicting, and included studies are too heterogenic to compare. Furthermore, various studies indicated a relation between high Hb levels and increased perinatal mortality. Therefore, we especially recommend attention to elevated Hb levels.

Target Audience

Obstetricians and gynecologists, family physicians.

Learning Objectives

After completing this activity, the learner should be better able to describe how Hb levels affect mode of delivery and short-term neonatal outcome, and identify abnormal Hb levels and propose appropriate treatment and monitoring recommendations.

Maternal hemoglobin level and its relation to fetal distress, mode of delivery, and short-term neonatal outcome: a retrospective cohort study

Aim: We aimed to investigate if the risk of fetal distress during term labor is related to the intrapartum maternal hemoglobin (Hb) level. Second, we investigated the relation between mode of delivery, reason for instrumental delivery and short-term neonatal outcome and maternal Hb. Third, we aimed to identify factors influencing intrapartum maternal Hb level.Methods: A retrospective cohort study was performed in a tertiary hospital in The Netherlands, including data from women who gave birth between 2009 and 2016. To determine whether the likelihood of fetal distress to occur was dependent on intrapartum Hb, multivariate regression models were run with intrapartum Hb as the main independent variable of interest. Hb was used as a continuous value. We repeated this procedure for the likelihood of instrumental vaginal delivery (IVD), cesarean section (CS), 5-min Apgar score < 7, and umbilical cord arterial pH ≤ 7.05 to occur. Also, we identified factors influencing intrapartum Hb level using linear regression analysis.Results: Data of 9144 patients were analyzed. Intrapartum Hb did not contribute to the prediction of the likelihood of fetal distress, IVD for nonprogressive labor, CS for fetal condition, 5-min Apgar score < 7, and pHa ≤ 7.05. However, there was a unique statistically significant contribution of Hb to the prediction of the likelihood of IVD for any reason and IVD for fetal distress and CS for any reason and CS for nonprogressive labor. IVD for fetal distress was related to a higher intrapartum Hb level, whereas CS for nonprogressive labor was related to a lower intrapartum Hb level. Intrapartum Hb level was influenced by maternal age, ethnicity, parity, fetal sex, and birth weight.Conclusions: The risk of fetal distress and adverse neonatal outcome is not related to intrapartum Hb levels. However, our data suggest that mode of delivery is dependent on intrapartum Hb, as shown in a large tertiary population. We recommend further investigating this relation in a large prospective study.

Gestation-Specific Changes in the Anatomy and Physiology of Healthy Pregnant Women: An Extended Repository of Model Parameters for Physiologically Based Pharmacokinetic Modeling in Pregnancy

BACKGROUND

In the past years, several repositories for anatomical and physiological parameters required for physiologically based pharmacokinetic modeling in pregnant women have been published. While providing a good basis, some important aspects can be further detailed. For example, they did not account for the variability associated with parameters or were lacking key parameters necessary for developing more detailed mechanistic pregnancy physiologically based pharmacokinetic models, such as the composition of pregnancy-specific tissues.

OBJECTIVES

The aim of this meta-analysis was to provide an updated and extended database of anatomical and physiological parameters in healthy pregnant women that also accounts for changes in the variability of a parameter throughout gestation and for the composition of pregnancy-specific tissues.

METHODS

A systematic literature search was carried out to collect study data on pregnancy-related changes of anatomical and physiological parameters. For each parameter, a set of mathematical functions was fitted to the data and to the standard deviation observed among the data. The best performing functions were selected based on numerical and visual diagnostics as well as based on physiological plausibility.

RESULTS

The literature search yielded 473 studies, 302 of which met the criteria to be further analyzed and compiled in a database. In total, the database encompassed 7729 data. Although the availability of quantitative data for some parameters remained limited, mathematical functions could be generated for many important parameters. Gaps were filled based on qualitative knowledge and based on physiologically plausible assumptions.

CONCLUSION

The presented results facilitate the integration of pregnancy-dependent changes in anatomy and physiology into mechanistic population physiologically based pharmacokinetic models. Such models can ultimately provide a valuable tool to investigate the pharmacokinetics during pregnancy in silico and support informed decision making regarding optimal dosing regimens in this vulnerable special population.

Characterization of the hemodynamic wall shear stresses in human umbilical vessels from normal and intrauterine growth restricted pregnancies

Significant reductions in blood flow and umbilical diameters were reported in pregnancies affected by intrauterine growth restriction (IUGR) from placental insufficiency. However, it is not known if IUGR umbilical blood vessels experience different hemodynamic wall shear stresses (WSS) compared to normal umbilical vessels. As WSS is known to influence vasoactivity and vascular growth and remodeling, which can regulate flow rates, it is important to study this parameter. In this study, we aim to characterize umbilical vascular WSS environment in normal and IUGR pregnancies, and evaluate correlation between WSS and vascular diameter, and gestational age. Twenty-two normal and 21 IUGR pregnancies were assessed via ultrasound between the 27th and 39th gestational week. IUGR was defined as estimated fetal weight and/or abdominal circumference below the 10th centile, with no improvement during the remainder of the pregnancy. Vascular diameter was determined by 3D ultrasound scans and image segmentation. Umbilical artery (UA) WSS was computed via computational flow simulations, while umbilical vein (UV) WSS was computed via the Poiseuille equation. Univariate multiple regression analysis was used to test for the differences between normal and IUGR cohort. UV volumetric flow rate, UA and UV diameters were significantly lower in IUGR fetuses, but flow velocities and WSS trends in UA and UV were very similar between normal and IUGR groups. In both groups, UV WSS showed a significant negative correlation with diameter, but UA WSS had no correlation with diameter, suggesting a constancy of WSS environment and the existence of WSS homeostasis in UA, but not in UV. Despite having reduced flow rate and vascular sizes, IUGR UAs had hemodynamic mechanical stress environments and trends that were similar to those in normal pregnancies. This suggested that endothelial dysfunction or abnormal mechanosensing was unlikely to be the cause of small vessels in IUGR umbilical cords.

Maternal cardiac function at 35-37 weeks' gestation: relationship with birth weight

OBJECTIVE

To evaluate the relationship between maternal cardiovascular parameters and neonatal birth weight and examine the potential value of these parameters in improving the prediction of small-for-gestational-age (SGA) and large-for-gestational-age (LGA) neonates provided by maternal characteristics and medical history.

METHODS

In 2835 singleton pregnancies maternal characteristics and medical history were recorded and maternal cardiovascular parameters were measured. The observed measurements of cardiovascular parameters were expressed as multiples of the normal median (MoM) values after adjustment for those characteristics found to provide a substantial contribution to their measurement. Regression analysis was used to determine the significance of association between the normalized values of the cardiovascular parameters with birth-weight Z-score. Multivariable logistic regression analysis was then used to determine if the maternal factors, fetal biometry and maternal cardiovascular parameters had a significant contribution to predicting SGA and LGA neonates. The performance of screening was determined by the area under receiver-operating characteristics curves (AUC).

RESULTS

In the study population there were significant positive associations between maternal cardiac output and heart rate with neonatal birth-weight Z-score, and significant negative associations between total peripheral resistance and mean arterial pressure (MAP) with neonatal birth-weight Z-score. In pregnancies delivering SGA neonates (n = 249 (8.8%)), cardiac output and heart rate were lower and total peripheral resistance and MAP were higher, whereas in pregnancies delivering LGA neonates (n = 292 (10.3%)) cardiac output and heart rate were higher and total peripheral resistance and MAP were lower. The performance of screening for delivery of SGA neonates achieved by maternal characteristics and fetal biometry was not improved by the measurement of maternal cardiovascular parameters. There was a small but significant improvement in the performance of screening for delivery of LGA neonates by maternal factors and fetal biometry with the addition of maternal heart rate (comparison of AUC, P = 0.0095).

CONCLUSIONS

There are significant associations between maternal cardiac output, heart rate, total peripheral resistance and MAP and neonatal birth-weight Z-score; such findings reflect the close relationship between maternal cardiac function and fetal demands. However, assessment of these parameters at 35-37 weeks' gestation is unlikely to improve substantially the performance of screening for SGA or LGA neonates provided by a combination of maternal factors and fetal biometry. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

[The role of oxidative stress in placental-related diseases of pregnancy]

In normal pregnancies, the earliest stages of development take place in a low oxygen (O₂) environment. This physiological hypoxia of the early gestational sac protects the developing fetus against the deleterious and teratogenic effects of O₂free radicals. Oxidative stress is manifested at the maternal-fetal interface from early pregnancy onwards. In early pregnancy, a well-controlled oxidative stress plays a role in modulating placental development, functions and remodelling. Focal trophoblastic oxidative damage and progressive villous degeneration trigger the formation of the fetal membranes, which is an essential developmental step enabling vaginal delivery. Our data have demonstrated that the first trimester placenta in humans is histiotrophic and not haemochorial. The development and maintenance of a physiological O₂ gradient between the uterine and fetal circulations is also essential for placental functions, such as transport and hormonal synthesis. Pathological oxidative stress arises when the production of reactive O₂ species overwhelms the intrinsic anti-oxidant defences causing indiscriminate damage to biological molecules, leading to loss of function and cell death. We here review the role of oxidative stress in the pathophysiology of miscarriage, pre-eclampsia and fetal growth restriction.

Fibrinogen, an endogenous ligand of Toll-like receptor 4, activates monocytes in pre-eclamptic patients

Pre-eclampsia (PE) remains the leading cause of pregnancy-associated mortality and morbidity, urging the need for a better understanding of its aetiology and pathophysiological progression. A key characteristic of PE is a systemic, exaggerated, inflammatory condition involving abnormal cytokine levels in serum, altered immune cell phenotype and Th1/Th2-type immunological imbalance. However, it is unknown how this heightened inflammatory condition manifests. We previously reported increased expression of the lipopolysaccharide receptor, Toll-like receptor 4 (TLR4), on monocytes from PE patients compared with normotensive, pregnant patients (NP). This upregulation of TLR4 on PE monocytes was accompanied by a hyper-responsiveness to bacterial TLR4 ligands. To determine whether non-microbial, endogenous TLR4 ligands also activate monocytes from PE patients, we investigated the expression of host-derived TLR4 ligands and the response of monocytes to these endogenous ligands. Plasma levels of fibrinogen - but not fibronectin or heparan sulphate - were higher in PE patients than in NP. Exposure to fibrinogen was associated with significantly increased production of inflammatory cytokines by monocytes from PE patients. Interestingly, this effect was not observed with NP monocytes. Our findings suggest that the fibrinogen-TLR4 axis might play an important role in the atypical activation of monocytes observed in PE patients that may contribute to the exaggerated inflammatory condition.

Rheological and physiological consequences of conversion of the maternal spiral arteries for uteroplacental blood flow during human pregnancy

Physiological conversion of the maternal spiral arteries is key to a successful human pregnancy. It involves loss of smooth muscle and the elastic lamina from the vessel wall as far as the inner third of the myometrium, and is associated with a 5–10-fold dilation at the vessel mouth. Failure of conversion accompanies common complications of pregnancy, such as early-onset preeclampsia and fetal growth restriction. Here, we model the effects of terminal dilation on inflow of blood into the placental intervillous space at term, using dimensions in the literature derived from three-dimensional reconstructions. We observe that dilation slows the rate of flow from 2 to 3 m/s in the non-dilated part of an artery of 0.4–0.5 mm diameter to approximately 10 cm/s at the 2.5 mm diameter mouth, depending on the exact radius and viscosity. This rate predicts a transit time through the intervillous space of approximately 25 s, which matches observed times closely. The model shows that in the absence of conversion blood will enter the intervillous space as a turbulent jet at rates of 1–2 m/s. We speculate that the high momentum will damage villous architecture, rupturing anchoring villi and creating echogenic cystic lesions as evidenced by ultrasound. The retention of smooth muscle will also increase the risk of spontaneous vasoconstriction and ischaemia–reperfusion injury, generating oxidative stress. Dilation has a surprisingly modest impact on total blood flow, and so we suggest the placental pathology associated with deficient conversion is dominated by rheological consequences rather than chronic hypoxia.

Maternal cardiac function in fetal growth-restricted and non-growth-restricted small-for-gestational age pregnancies

OBJECTIVE

To compare maternal cardiac function in women with intrauterine growth restriction (IUGR) to those with small-for-gestational age (SGA) pregnancies (non-IUGR).

METHODS

This was a cross-sectional study involving maternal echocardiography and uterine, umbilical and fetal middle cerebral artery Doppler assessment in 52 normotensive women at 20-36 weeks' gestation with SGA fetuses (26 IUGR and 26 non-IUGR).

RESULTS

In the IUGR (compared to the non-IUGR) group, maternal cardiac output (CO) was lower (4.7 vs. 6.1 L/min, P<0.001) and total vascular resistance (TVR) was higher (1444 vs. 1088 dynes/s/cm5, P<0.001). The lower CO was due to a lower preload, demonstrated by a reduced stroke volume (59.9 vs. 73.6 mL, P<0.01) and smaller left atrial diameter (LAD) (31.5 vs. 34.1 mm, P=0.01). Mean arterial pressure and diastolic function were similar between the groups. Logistic regression and receiver-operating characteristics curve analysis for detection of IUGR demonstrated that a model using TVR, LAD, fetal middle cerebral artery pulsatility index and gestational age, had a sensitivity of 96.2% and a specificity of 84.6%.

CONCLUSIONS

Maternal echocardiography can provide a very sensitive tool for identifying IUGR pregnancies.

Maternal cardiac function in fetal growth restriction

OBJECTIVE

To assess the maternal central haemodynamics in normotensive women with pregnancies complicated by severe fetal growth restriction (FGR).

DESIGN

Cross-sectional study.

SETTING

A tertiary referral fetal medicine unit.

POPULATION

The study groups comprised 107 women with normal singleton pregnancies and 20 with singleton pregnancies complicated by FGR at 25-37 weeks. In the latter group, assessment was carried out within 10 days prior to their delivery. All the women were normotensive, without any medical problems.

METHODS

Two-dimensional and M-mode echocardiography of the left ventricle.

MAIN OUTCOME MEASURES

Maternal left ventricular systolic and diastolic function.

RESULTS

In the FGR group, compared with the normal group, there was increased total vascular resistance (TVR), reduced systolic function characterised by lower cardiac output, stroke volume, heart rate, ejection time and septal and lateral long-axis shortening. Mean arterial pressure (MAP) was not significantly different between the groups.

CONCLUSIONS

Severe FGR is associated with reduced maternal systolic function and increased TVR but no change in MAP. TVR may be a useful tool in the classification and management of FGR. The findings suggest that in FGR, there is increased blood viscosity due to lack of intravascular space expansion.

First trimester maternal blood rheology and pregnancy induced hypertension

This study evaluates the relationship between the first trimester assessment of maternal rheology and the subsequent development of pregnancy induced hypertension. This is a prospective observational study based in the Glasgow Royal Maternity Hospital, Scotland. From an original population of 744 consecutive antenatal attendees a total of 579 women were booked at less than 14 weeks' gestation. The main study group is a further subset comprising 251 primigravid women booking with a singleton pregnancy without essential hypertension. Previously published data from a group of non-pregnant women of similar age drawn from the same local community was used for external comparison. Blood samples were collected at the booking visit, from which fibrinogen, red cell aggregation, haematocrit and plasma, whole blood, relative and corrected viscosities were recorded. Information was obtained from the case notes in retrospect starting approximately 1 year after the first patients had first been recruited into the trial. The overall outcome of the pregnancies was noted with particular reference to pregnancy induced hypertension (PIH), birth weight, antepartum haemorrhage, pre-term labour, perinatal death, condition at delivery and neonatal complication. Our results show PIH is associated with a significantly raised mean blood viscosity and fibrinogen at time of booking. All significance disappears after adjustment for smoking, diastolic blood pressure and age. Viscosity is, however, only marginally non-significant (p = 0.07). In conclusion, blood rheology, in particular blood viscosity and fibrinogen, may play a predictive role in the development of pregnancy-induced hypertension. When combined with measurement of smoking and diastolic blood pressure at booking, these measurements could be used to calculate a risk score for the development of PIH, allowing targeting of antenatal care. Further data is required.

Pregnancy at high altitude: a hyperviscosity state

BACKGROUND

Pregnancy at high altitude has been associated with intrauterine growth restriction and preeclampsia. These conditions, at sea level, have been linked to increased hematocrit and blood viscosity. The aim of this study was to investigate the effect of high altitude on maternal hemorheology.

METHODS

This was a cross-sectional study. We examined 94 pregnant women at 10-38 weeks of gestation resident at high altitude (4370 m above sea level) and 75 at sea level, and 24 and 17 nonpregnant women at each altitude, respectively. Blood and plasma viscosity, hematocrit, plasma fibrinogen, albumin and total protein concentrations were determined in blood samples obtained after an overnight period of fasting.

RESULTS

Pregnancy at high altitude, compared to sea level, is characterized by higher hematocrit, blood viscosity (at high shear rate), plasma viscosity, total protein and fibrinogen concentrations (25%, 38%, 7%, 13.3% and 25%, respectively) and 6% lower albumin concentration. Nonpregnant women at high altitude, compared to sea level, had higher hematocrits, blood viscosity, plasma viscosity, total protein and fibrinogen concentrations (25%, 55%, 18%, 26% and 98%, respectively) and 13% lower albumin concentration.

CONCLUSION

Pregnancy at high altitude compared to sea level is characterized by increased blood viscosity as a result of increased hematocrit and plasma viscosity.

Haemorheological adaptation during pregnancy in a Latin American population

OBJECTIVE

To investigate haemorheological changes during pregnancy in a Latin American population and compare to previously published data from Caucasian populations.

DESIGN

Cross-sectional study.

POPULATION

75 pregnant women at 10-36 wk of gestation and 17 non-pregnant female controls in Lima, Peru. All the women and their ancestors for three generations were born and lived at sea level.

METHODS

Viscosity, haematocrit and plasma fibrinogen, albumin and total protein concentrations were determined in blood samples obtained after an overnight period of fasting.

RESULTS

At 10 wk of gestation, total protein concentration and plasma viscosity were above non-pregnant levels by about 15% and subsequently decreased linearly with gestation. Fibrinogen concentration was increased in the first trimester; it then decreased to a nadir at about 20 wk and subsequently increased. Albumin concentration decreased linearly with gestation. Haematocrit decreased from pre-pregnancy levels at 10 wk to a nadir at about 26 wk. Blood viscosity increased in the first trimester and then decreased with gestation to a nadir at about 26 wk.

CONCLUSION

In the first trimester of pregnancy blood and plasma viscosity are increased and they subsequently fall with advancing gestation. Plasma viscosity reflects the changes in total protein concentration, and blood viscosity is dependent on the interplay of changes in plasma viscosity and haematocrit.

The influence of maternal erythrocyte deformability on fetal growth, gestational age and birthweight

The increase in blood viscosity during pregnancy reduces maternal-fetal blood flow, which can lead to fetal hypoxia and acidosis. These factors have been related to a reduction in fetal growth and to premature births. We carried out a longitudinal study of 36 normal-term gestations at different stages of the pregnancy. We analyzed the erythocyte deformability, the intraerythocyte viscosity and the plasma viscosity in the mother, as well as the relation of these parameters to fetal growth (biparietral diameter (BPD) and length of the femur), birthweight, gestational age at birth and the Agpar score. The results obtained were as follows: from weeks 25 to 36 of pregnancy (30.9 (SD 2 weeks)) there occurs a significant increase in maternal erythocyte rigidity (p < 0.05) (despite the compensatory decrease in intracellular viscosity). This increase is very significantly related to the fetal biparietral diameter (r = -0.50, p < 0.01), the length of the fetal femur (r = -0.48, p < 0.02), gestational age at birth (r = -0.73, p < 0.0001, birthweight (r = -0.63, p < 0.001) and the Agpar score 5 minutes after birth (r = 0.67, p < 0.001). Our conclusions are that the reduction in erythocyte deformability (which we attribute to alterations in the fluidity or elasticity of its membrane) and the factors that increase the aggregation capacity of the red cells (modulators of blood viscosity and of blood flow in the placental intervillous space) are risk factors for reduced fetal growth, lower birthweight and lower gestational age at birth. By avoiding maternal hematocrit levels higher than 36% we could improve uteroplacental perfusion, fetal growth and perinatal results.

Preeclampsia: haemostatic status and the short-term effects of methyldopa and isradipine therapy

OBJECTIVE

To determine the haemostatic status in preeclampsia and to investigate the effects of short-term use of anti-hypertensive drugs, methyldopa and isradipine.

METHODS

Thirty preeclamptic (PE) women admitted to the hospital for observation and treatment were randomized to receive either methyldopa or isradipine for 2 weeks. Their blood pressure were monitored for 24 h before treatment and again at 7 days and 14 days after treatment using the programmable automated ambulatory blood pressure (ABP) monitoring system. Blood sampling was performed before commencement of anti-hypertensive treatment, 7 days and 14 days after treatment and the haemostatic parameters studied was compared before treatment with normal pregnancy and the effect of anti-hypertensive treatment. Nineteen normal pregnant subjects with a total of 30 blood sampling at various gestation and good pregnancy outcome served as controls. The following haemostatic parameters were determined; thrombelastography, fibrinogen, antithrombin III (ATIII), thrombin-antithrombin (TAT)-complex, beta-thromboglobulin (beta-TG), plasminogen activators (t-PA, u-PA), plasminogen activator inhibitors (PAI-1, PAI-2), and plasminogen.

RESULTS

Significant lowering of blood pressure was evident at Days 7 and 14 of therapy with either methyldopa or isradipine. Increased mean plasma fibrinogen and decreased ATIII levels were seen in preeclampsia together with decreased u-PA and t-PA activity levels in contrast to increased t-PA antigen and beta-TG. No significant differences were seen for TAT-complex, PAI-1, plasminogen and D-dimer levels although their mean levels were higher than observed in non-pregnant subject except for PAI-2, the level was significantly reduced when compared with normal pregnancy. Two-way analysis of variance showed no significant alteration on all haemostatic parameters studied in preeclamptic women receiving either methyldopa or isradipine after 7 and 14 days of therapy.

CONCLUSION

Enhance activation of coagulation was observed together with raised fibrinolysis in normal pregnancy and PE. However, in PE a further reduction in ATIII, u-PA and PAI-2 with increased fibrinogen and platelet activation could lead to an imbalance in the coagulation/fibrinolysis equilibrium which favours fibrin deposition. All these changes seen in PE including the coagulation kinetics were not altered by the short term effects of methyldopa and isradipine even though significantly lowered blood pressure were observed during therapy.

Lipoproteins in pregnant women before and during delivery: influence on neonatal haemorheology

AIMS

To investigate whether the lipid profile of pregnant women during parturition differs from the profile at previous stages of pregnancy and to determine the effects of maternal lipid changes on fetal or neonatal haemorheology.

METHODS

Sixty pregnant women were studied, divided into two groups. Group 1 contained 30 women of mean age of 27 (SD 3) years and gestational age > 38 weeks in whom delivery had not yet begun; all these pregnancies followed an uncomplicated course and there was no evidence of any fetal pathology from previous obstetric examinations. All the women reached term and birth weight was 3340 (350) g. Group 2 contained women of mean age 26 (4) years, in whom delivery was ongoing, all of whose pregnancies reached term. The following variables were determined in all cases: total cholesterol, triglycerides, high density lipoproteins (HDL), low density lipoproteins (LDL), free fatty acids and phospholipids, and apoprotein A (apo-A) and apoprotein B (apo-B). Serum and plasma viscosity was measured with a capillary viscosimeter.

RESULTS

The apo-B/apo-A and HDL/apo-A ratios increased during delivery, indicating that in pregnant women these atherogenic indices are raised during delivery compared with previous gestational stages. Significant correlation coefficients were obtained between maternal lipids (triglycerides, total cholesterol, LDL, total cholesterol/HDL, and LDL/HDL) and plasma viscosity in the neonate.

CONCLUSIONS

Plasma atherogenic indices increase progressively until birth. These changes have implications for neonatal haemorheology because they cause an increase in plasma viscosity.

Relationship of blood rheology to lipoprotein profile during normal pregnancies and those with intrauterine growth retardation

AIMS

The effects on fetal growth of hyperlipidaemia in pregnancy are not well understood at present. In this study the different lipid fractions in normal pregnancies and pregnancies complicated by intrauterine growth retardation (IUGR) were determined and related to changes in plasma and serum viscosity.

METHODS

Two groups of pregnant women were studied. Group 1 consisted of 35 healthy pregnant women aged between 21 and 38 years with no previous pathology and a normal pregnancy to term. Group 1 patients were studied at four periods defined at the start of the study: (1) < or = 17 weeks; (2) 18-24 weeks; (3) 25-32 weeks, (4) > or = 33 weeks. Group 2 consisted of 24 pregnant women aged between 16 and 34 years with ultrasound diagnosed IUGR confirmed after birth. Plasma lipids and plasma and serum viscosity were measured.

RESULTS

Plasma triglycerides, low density lipoprotein cholesterol, and total cholesterol increased progressively throughout pregnancy, with significantly higher values after week 25. Apolipoprotein A (ApoA) and triglyceride concentrations were significantly lower in the IUGR group than in the normal group. The HDL/ApoA ratio was greater in the IUGR group than in the control group, as was the ApoB/ApoA ratio. There were no differences in the other lipids. Plasma and serum viscosity was higher in the IUGR group than in the normal group.

CONCLUSIONS

Haemorheological modifications in the IUGR group are partly secondary to changes in high density lipoprotein metabolism and the competitive inhibition of fibrinolysis by ApoB, which is increased in pregnancies with IUGR. Changes in ApoA, and more specifically in the ApoB/ApoA ratio, could be good markers for the early detection of IUGR.

Blood rheology and albumin excretion in diabetic pregnancy

Blood rheology is altered in diabetes and also in non-diabetic pregnant women. The cumulative effect of hyperfiltration, abnormal rheology of pregnancy, and diabetes could be one mechanism contributing to increased intraglomerular pressure and albuminuria in diabetic pregnancy. We conducted a prospective study of 22 Type 1 (insulin-dependent) diabetic patients and 22 non-diabetic women to determine if there was an association of altered blood rheology on glomerular function in diabetic pregnancy. Albumin excretion showed no increment with increasing gestation and was similar in diabetic and non-diabetic women throughout pregnancy (first trimester: 5.0 (3.0-14.0) vs 5.8 (3.7-10.7) mg l-1, p = 0.89; second trimester: 6.0 (5.0-12.0) vs 5.1 (3.6-10.4) mg l-1, p = 0.25; third trimester: 7.5 (3.5-16.0) vs 4.9 (2.9-7.3) mg l-1, p = 0.18). Red cell aggregation index increased in both groups between the first and third trimesters (diabetic patients: mean difference 2.0; Cl: 1.0-2.9, p = 0.003, and control patients: mean difference 2.3, Cl: 1.0-3.5, p = 0.002). Fibrinogen levels were significantly higher between the third and first trimesters in diabetic patients (mean difference 0.7, Cl: 0.2-1.3 g l-1, p = 0.006). Pregnancy, therefore, was associated with increased red cell aggregation, related in part to increased fibrinogen levels but the extent of change was similar in diabetic and nondiabetic women and appeared to have no adverse effect on glomerular function in pregnant insulin-dependent diabetic women.

Nifedipine treatment in preeclampsia reverts the increased erythrocyte aggregation to normal

OBJECTIVES

Our objectives were to assess erythrocyte aggregation in hypertensive pregnancy and to evaluate the effect of the antihypertensive treatment on it.

STUDY DESIGN

The mean entity of erythrocyte aggregation was determined by an automatic aggregometer in 57 pregnant women: 20 normotensive, seven chronically hypertensive, 10 chronically hypertensive with superimposed preeclampsia, and 20 with preeclampsia. Ten of the latter were subsequently treated by 40 mg/day oral nifedipine; the other 10 by 400 mg/day oral labetalol, to keep diastolic blood pressure < 90 mm Hg. Also, patients with superimposed preeclampsia were treated with 40 mg/day oral nifedipine.

RESULTS

Erythrocyte aggregation was increased in all the hypertensive pregnant patients compared with the normotensive pregnant controls, regardless of both the onset (chronic or pregnancy-induced) of hypertension and the status of plasma macromolecules. Antihypertensive treatment with labetalol significantly reduced the aggregability of erythrocytes, whereas treatment with nifedipine reverted it to normal.

CONCLUSIONS

Increased erythrocyte aggregation may be due to either conformational changes of the membrane occurring during hypertension or a redistribution of the ionic charges on the two surfaces of the membrane. The effect of nifedipine by restoring the ionic charges may be due to this latter event.

Hemodynamic and hemorheological profiles in women with proteinuric hypertension of pregnancy and in pregnant controls

We obtained blood samples from 52 patients with pre-eclampsia and from 40 pregnant controls for measurement of plasma urate levels, hematocrit, white cell count and various hemorheological parameters. We also used impedance cardiography to measure cardiac output in both groups and from the results derived values for total peripheral resistance and oxygen transport. Central venous pressure was measured with a superior vena cava catheter in patients with pre-eclampsia but not in controls. Women with pre-eclampsia had significantly lower cardiac output and central venous pressure when compared with a control group. A modest correlation was observed between central venous pressure and cardiac output. The majority of pre-eclamptic patients had significantly raised hematocrit, leucocyte count, uric acid and red cell aggregation. Red cell deformability was significantly decreased in patients with pre-eclampsia. Most patients with severe pre-eclampsia (BP diast. greater than 100 mmHg) had a low Antithrombin III and colloid osmotic pressure level. The leucocyte count was raised when compared with the women with moderate pre-eclampsia. Oxygen delivery was reduced in patients with pre-eclampsia because of impaired rheological properties of their blood.

Maternal blood viscosity and uteroplacental blood flow velocity waveforms in normal and complicated pregnancies

According to the Poiseuille-Hagen law, viscosity influences flow resistance. A possible effect of blood viscosity upon the resistance index of the uteroplacental circulation as measured by continuous wave Doppler ultrasound was investigated in 50 pregnant women. It was found that blood viscosity variables explained only about 10% of the variation in the resistance index in all patients, which was not statistically significant. It is suggested, therefore, that the vascular contribution to flow resistance may be more important.

Whole blood viscosity during normal pregnancy

In a serial study the changes in whole blood viscosity at different shear rates and its major determinants were determined in 24 healthy women with normal pregnancies. Whole blood viscosity and plasma viscosity were measured with a rotational viscometer. Red cell aggregation was measured by syllectometry. During normal pregnancy we found a decrease in whole blood viscosity at all shear rates until 29 weeks gestation, followed by a smaller increase between 30 and 37 weeks, which was most pronounced at higher shear rates, especially in nulliparae. The changes in whole blood viscosity were to a great extent determined by the changes in haematocrit and plasma viscosity. Haematocrit was more important for whole blood viscosity at lower shear rates, while plasma viscosity had more influence on high shear blood viscosity. The continuous increase in red cell aggregation had no demonstrable influence on low shear blood viscosity as measured in vitro in a rotational viscometer.

Blood rheology and pregnancy

Pregnancy is a hypervolaemic situation with early expanded plasma volume, a high cardiac output and a decrease in the vascular and rheological resistance. The increase in plasma volume correlates better with fetal size than maternal size. The hypervolaemic and vasodilated state that accompanies normal pregnancy results in a high flow in the uterine arteries. In contrast, patients with PIH (pregnancy-induced hypertension) or placental insufficiency may have a contracted plasma volume secondary to diffuse vasoconstriction. In spite of the intense vasospasm and hypovolaemia, pre-eclampsia has generally a cardiac output which may be equal, higher or lower compared with non-eclamptic pregnancy. Hypovolaemia is reflected in a higher haematocrit than normal. In the case of a hypovolaemic state, haemoconcentration is associated with high red cell aggregation. In fetal distress and severe PIH, the rheological status (haemoconcentration and elevated red cell aggregation) has a high predictive value for perinatal complications. In patients with severe PIH, erythrocyte filtration is impaired. The increased leukocyte count in patients with PIH may occlude small vessels and could be a factor impairing intervillous blood flow. The increased erythrocyte rigidity may result from a re-distribution of cellular calcium metabolism (Blaustein concept). We conclude that there is an optimal haematocrit during pregnancy between 30% and 38%. The presence of a high haematocrit and in addition elevated red cell aggregation should alert the physician to an increased risk of fetal compromise.

Estrogen effects on plasma volume, arterial blood pressure, interstitial space, plasma proteins, and blood viscosity in sheep

In adult castrated ewes the infusion of 17 beta-estradiol for 3 weeks was associated with a 12% increase in body weight, a 20% increase in whole blood volume (mainly due to a 27% increase of plasma volume), a 13% decrease in mean arterial blood pressure, and a 40% increase in heart rate. The change in plasma volume correlated with the change in estradiol concentration (r = 0.72). Most of the fluid was retained in the interstitial space, as represented by a 6 kg weight gain, 10% of which was in the intravascular compartment. Whole blood and plasma viscosity increased 16% and 21%, respectively, thus reversing some of the blood volume effects toward a hyperdynamic cardiovascular state. We conclude that many of the cardiovascular and hematologic changes with estrogen administration are similar to the changes observed during pregnancy, with the proposed requirement of decrease in mean arterial blood pressure as a condition for blood volume expansion.

Microscopical morphology of the human placenta and its effects on oxygen diffusion: a morphometric model

A combination of stereological and physicochemical data was used to estimate the oxygen-diffusing capacity of the human term placenta. The effects on this morphometric diffusing capacity of isolated changes in placental structure were investigated by permitting volumes, surface areas and harmonic mean diffusion distances to deviate from normal baseline (term) values. Diffusion performance could be monitored effectively by estimating only three structural quantities. The most influential variable was the harmonic mean thickness of the villous membrane followed by the surface areas of villi and of fetal capillaries. Blood space volumes and plasma diffusion distances had negligible effects on diffusing capacity. Conclusions are discussed in the context of published findings on changes in placental anatomy which occur during gestation, abnormal pregnancies and pregnancies at high altitude.

Is maternal whole blood viscosity a factor in fetal growth?

Many authors have correlated changes in maternal hemodynamics during pregnancy with fetal growth. Sufficient plasma volume expansion in pregnancy seems mandatory for an optimal reproductive result. A correlation between rheological characteristics (low-shear whole blood viscosity and yield shear stress) and birthweight centiles was found in 26 third-trimester pregnancies. The level of statistical significance (P less than 0.05) was reached in nulliparous pregnancies but not in parous pregnancies. Measurements of whole blood viscosity at low shear rate and yield shear stress seem to provide information on the efficacy of placental perfusion. There have been reports in the literature to support the assumption of the prevalence of low-shear circumstances in the intervillous space. The hypothesis is put forward that, during pregnancy, the changes in maternal hemodynamics influence fetal growth by their impact on the flow through the placenta.

Erythrocyte filterability and fetal development in normal pregnancy

The relationship between maternal erythrocyte filterability determined in late pregnancy and infant birth weight was studied in uncomplicated pregnancy. There was a significant positive correlation (r = 0.7671, p less than 0.005). Maternal erythrocyte filterability is suggested to be an indicator of flow state of the placental microcirculation, which affects fetal development.

Blood rheology in pre-eclampsia and intrauterine growth retardation: effects of blood pressure reduction with labetalol

Blood viscosity ( Contraves L S 30) and its determinants were measured in 23 patients with mild/moderate pre-eclampsia, 10 patients with intrauterine growth retardation and 22 control subjects, matched for age and gestation. Both abnormal groups had a significantly increased blood viscosity at high shear rate (94 s-1) associated with increased haematocrit. Fibrinogen levels were also increased, but there were no significant differences between groups in plasma viscosity, low shear viscosity (0.94 s-1) or red cell deformability, measured by a low-shear washed cell system of filtration through 5-micron pore diameter Nuclepore filters. In the pre-eclamptic group, measurements were repeated after 1-2 weeks in nine patients treated with labetalol (a combined alpha and beta adrenergic blocker) and in 10 patients treated with bed rest. Labetalol reduced blood pressure but no change in rheology was seen in either group. Control of blood pressure by labetalol does not adversely affect rheology, in contrast to diuretics which are known to cause haemoconcentration and increased blood viscosity.

Erythrocyte aggregation during normal pregnancy

Red blood cell aggregation induced by fibrinogen is a major determinant of the non-Newtonian flow behavior of blood and has been suggested as a possible contributing factor for thrombogenesis. Given the elevated fibrinogen levels and the incidence of thrombotic accidents in pregnancy, a study was designed to assess red blood cell aggregation at selected gestational periods. Three separate in vitro aggregation assays were used: (1) aggregation half time, (2) zeta sedimentation ratio, and (3) microscopic aggregation index. Our results indicate that red blood cell aggregation is increased throughout normal pregnancy (i.e., at 10, 25, and 36 weeks and during labor) in comparison to that in nonpregnant women. Significant correlations between plasma fibrinogen concentration and zeta sedimentation ratio (p less than 0.001) or aggregation half time (p less than 0.02) were demonstrated, but the correlation coefficient for the microscopic aggregation index technique did not reach significance (p greater than 0.20). Type O-positive red blood cells suspended in plasma from pregnant women also exhibited increased aggregation (p less then 0.001), thus suggesting plasma rather than cellular factors for the enhanced aggregation. Possible influences of abnormal fibrinogen structure during pregnancy are considered and the implications of increased red blood cell aggregation vis-à-vis altered blood viscosity are discussed.