Doppler sonography of the uterine and the cubital arteries in normal pregnancies, preeclampsia and intrauterine growth restriction: evidence for a systemic vessel involvement

Maternal vascular responses to hypoxia in a rat model of intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a common pregnancy complication and is a leading cause of fetal morbidity and mortality. Placental hypoxia contributes to adverse fetal consequences, such as IUGR. Exposing pregnant rats to hypoxia can lead to IUGR; however, assessment of maternal vascular function in a rat model of hypoxia, and the mechanisms that may contribute to adverse pregnancy outcomes, has not been extensively studied. We hypothesized that exposing pregnant rats to hypoxia will affect maternal systemic vascular function and increase the uterine artery resistance index (RI), which will be associated with IUGR. To test this hypothesis, pregnant rats were kept in normoxia (21% O₂) or hypoxia (11% O₂) from gestational day (GD) 6 to 20 Maternal blood pressure, uteroplacental resistance index (RI) (ultrasound biomicroscopy), and vascular function (wire myography) were assessed in uterine and mesenteric arteries. Fetal weight was significantly reduced (P < 0.001), while maternal blood pressure was increased (P < 0.05) in rats exposed to hypoxia. Maternal vascular function was also affected after exposure to hypoxia, including impaired endothelium-dependent vasodilation responses to methacholine in isolated uterine arteries (pEC₅₀ normoxia: 6.55 ± 0.23 vs. hypoxia: 5.02 ± 0.35, P < 0.01) and a reduced uterine artery RI in vivo (normoxia: 0.63 ± 0.04 vs. hypoxia: 0.53 ± 0.01, P < 0.05); associated with an increase in umbilical vein RI (normoxia: 0.35 ± 0.02 vs. hypoxia: 0.45 ± 0.04, P < 0.05). These data demonstrate maternal and fetal alterations in vascular function due to prenatal exposure to hypoxia. Further, although there was a compensatory reduction in uterine artery RI in the hypoxia groups, this was not sufficient to prevent IUGR.

Association between uterine artery Doppler blood flow changes and arterial wall elasticity in pregnant women

INTRODUCTION

Uterine artery (UtA) Doppler velocimetry changes and increased arterial stiffness are associated with preeclampsia. We aimed to investigate the relation between UtA velocimetry changes and arterial stiffness in pregnant women.

METHODS

Doppler velocimetry and photoplethysmographic digital pulse wave analysis (DPA) were performed in 173 pregnant women in the second or the third trimester, where UtA Doppler pulsatility index (PI), diastolic notching, and UtA score (UAS) combining notching and high PI were calculated. DPA stiffness parameters representing large arteries were ejection elasticity index (EEI) and b/a, small arteries dicrotic index (DI) and d/a, and global stiffness the aging index (AI).

RESULTS

One hundred and thirty women had normal Doppler and 43 had diastolic notching, of whom nine had high PI. DI indicated increased stiffness in small arteries when notching was present (p = 0.044) and showed a significant but weak correlation to UAS (p = 0.025, tau 0.12). EEI and b/a indicated increased large artery stiffness (p ≤0.014), d/a small artery stiffness (p = 0.023), and AI a systemic stiffness (p = 0.040) when high PI.

CONCLUSION

High UtA PI was associated with increased systemic arterial stiffness, whereas notching was related to increased stiffness in small arteries only. This indicates pathophysiological differences between the two Doppler parameters.

Differences in cardiovascular function comparing prior preeclamptics with nulliparous controls

OBJECTIVE

The objective of the current study was to evaluate cardiovascular function; including blood pressure, cardiac output, pulse wave velocity and vascular compliance in nonpregnant nulliparous women compared to women with a history of preterm preeclampsia.

STUDY DESIGN

This was a case control study. Blood pressure was measured using the Finapres Pro. Baseline cardiac output was determined by echocardiography. Pulse wave velocity was estimated using simultaneous electrocardiographic tracings and ultrasound determined arterial flow waveforms and calculated as estimated distance divided by the time interval between EKG r-wave peak and ultrasound derived peak popliteal artery flow. During volume challenge, 500mL of lactated Ringers solution was infused through an indwelling antecubital catheter over 10min. Cardiac output and blood pressure during and 15min after the infusion were estimated using the Finapres Pro.

MAIN OUTCOME MEASURES

Indices of arterial stiffness and vascular compliance.

RESULTS

Previous preeclamptics exhibited a significant increase in pulse pressure and cardiac output in response to volume challenge when compared with nulliparous controls. Prior preeclamptics had a strong positive correlation between blood pressure indices (r=0.50-0.68, p⩽0.01) and pulse pressure (r=0.58, P=0.008) with pulse wave velocity that was not evident in control women.

CONCLUSIONS

In women with prior preterm preeclampsia a relationship between blood pressure, intravascular volume and arterial stiffness, is evident in the nonpregnant state and in the absence of hypertension or overt cardiovascular disease. This supports an overarching hypothesis that nonpregnant physiology is an important contributor to pregnancy adaptations.

Placental lesions associated with maternal underperfusion are more frequent in early-onset than in late-onset preeclampsia

OBJECTIVE

Preeclampsia (PE) has been classified into early- and late-onset disease. These two phenotypic variants of PE have been proposed to have a different pathophysiology. However, the gestational age cut-off to define "early" vs. "late" PE has varied among studies. The objective of this investigation was to determine the prevalence of lesions consistent with maternal underperfusion of the placenta in patients with PE as a function of gestational age.

STUDY DESIGN

A nested case-control study of 8307 singleton pregnant women who deliver after 20 weeks of gestation was constructed based on a cohort. Cases were defined as those with PE (n=910); controls were pregnant women who did not have a hypertensive disorder in pregnancy (n=7397). The frequency of maternal underperfusion of the placenta (according to the criteria of the Society for Pediatric Pathology) was compared between the two groups. Logistic regression was used for analysis. Estimated relative risks (RRs) were calculated from odds ratios.

RESULTS

1) The prevalence of lesions consistent with maternal underperfusion was higher in patients with PE than in the control group [43.3% vs. 15.9%, unadjusted odds ratio 4.0 (95% CI 3.5-4.7); P<0.001]; 2) the estimated RR of maternal underperfusion lesions in PE was higher than in the control group [RR=2.8 (95% CI 2.5-3.0)]; 3) the lower the gestational age at delivery, the higher the RR for these lesions; 4) early-onset PE, regardless of the gestational age used to define it (<32, 33, 34, 35 or 37 weeks) had a significantly higher frequency of placental lesions consistent with maternal underperfusion than late-onset PE (P<0.001 for all).

CONCLUSIONS

1) The earlier the gestational age of preeclampsia at delivery, the higher the frequency of placental lesions consistent with maternal underperfusion; 2) our data suggest that demonstrable placental involvement as determined by pathologic examination differs in early- and late-onset preeclampsia; and 3) this phenomenon appears to be a continuum, and we could not identify a clear and unambiguous gestational age at which lesions consistent with underperfusion would not be present.

Medically indicated preterm birth: recognizing the importance of the problem

Preterm birth complicates over 500,000 births annually, affecting 12.5% of pregnancies in the United States. Much of the temporal increase in preterm birth (<37 weeks) over the past decade is largely driven by a concurrent temporal increase in medically indicated preterm birth. Maternal and fetal indications that prompt an intervention at preterm gestational ages include preeclampsia, intrauterine growth restriction, and placental abruption-conditions that constitute "ischemic placental disease." Ischemic placental disease is implicated in over one of every two indicated preterm births compared with less than one in five births at term. Comprehensive evaluation of risk factors, with careful consideration of heterogeneity in the syndrome of medically indicated preterm birth and ischemic placental disease may provide important clues to predict and consequently prevent preterm birth.

Nitric oxide and peroxynitrite platelet levels in women with small-for-gestational-age fetuses

OBJECTIVE

The placenta produces reactive oxygen species (ROS) including nitric oxide (NO) and peroxynitrite (ONOO(-)) that have pronounced effects on placental function. Excessive ROS production may occur in pathological pregnancies, such as those complicated by small-for-gestational-age (SGA) fetuses.

DESIGN

The aim of the present work was to study NO and ONOO(-) levels in platelets of pregnant women with SGA fetuses compared with a control group.

SETTING AND POPULATION

The study was performed on 30 pregnant women with SGA fetuses (SGA group) and on 30 healthy pregnant women (appropriate-for-gestational-age [AGA] group) matched for maternal and gestational age. All women included in this study were in the third trimester of pregnancy.

METHODS

Platelets were isolated by differential centrifugation. NO metabolites, after enzymatic conversion followed by the Griess reaction, were measured as nitrite by spectrophotometric detection. Peroxynitrite (ONOO(-)) levels were evaluated using the fluorescence probe 2,7-dichlorofluorescein diacetate (DCFDA).

MAIN OUTCOME MEASURES

The following determinations were made: platelet nitric oxide and peroxynitrite levels in the SGA group and controls; inducible nitric oxide synthase (iNOS), endothelial nitric oxide synthase (eNOS) and nitrotyrosine (N-Tyr) expression in the same groups.

RESULTS

Our results show that both platelet NO and ONOO(-) levels were significantly higher in the SGA group than in the controls.

CONCLUSION

Increased platelets levels of nitric oxide and peroxynitrite might play a role in the pathophysiology of intrauterine growth restriction. Further investigations are in progress to clarify if these molecules are pathogenetic factors, an epiphenomenon or a pathophysiological marker.

Plasma- and urine concentrations of nitrite/nitrate and cyclic Guanosinemonophosphate in intrauterine growth restricted and preeclamptic pregnancies

BACKGROUND

The Nitric Oxide (NO) system plays an important role in the establishment and maintenance of the feto-placental circulation. Research on the pathogenesis of preeclampsia in several studies has established the involvement of the NO-system in preeclampsia and fetal intrauterine growth restriction (IUGR). In the presented study we analyzed the urine and plasma concentrations of nitrite/nitrate, the stable endproducts of NO and its second messenger, cyclic Guanosinemonophosphate (cGMP) in normal, preeclamptic and IUGR pregnancies.

PATIENTS AND METHODS

In total 76 patients were investigated in a prospective study for repeated determination of plasma and urinary levels of nitrate/nitrite and cGMP: 49 patients with a normal course of pregnancy, 14 patients with fetal IUGR and 13 patients with preeclampsia were included into the study. Plasma and urine Nitrite/Nitrate-concentrations were determined using a Colorimetric Assay (Cayman Inc., USA), concentrations of the second messenger cGMP in plasma and urinary samples were determined with a J(125)-Radio-Immuno-Assay (ibl Inc., Germany). The Stat View Program (Abacus Concepts, Inc., Berkeley, CA, 1992-1998) was used for statistical analysis, a P value <0.05 was considered significant.

RESULTS

Analyzing the data with the Kruskall-Wallis test a significance was reached for Plasma Nitrite/Nitrate (P=0.0236), plasma cGMP (P=0.004) and urinary nitrite/nitrate (P=0.032). No significance was seen for urinary cGMP (P=0.656). Comparing normal and preeclamptic and normal and IUGR pregnancies the following significant differences were seen (Mann-Whitney U test): In preeclamptic pregnancies urine nitrite/nitrate concentration was significantly lower compared to normal pregnancies (P=0.009) No significant difference between normal and preeclamptic pregnancies for plasma nitrite/nitrate (P=0.819) and plasma-cGMP (P=0.072) could be observed. In IUGR pregnancies plasma nitrite/nitrate and the plasma-cGMP concentrations were both significantly lower compared to normal pregnancies (P=0.0077 and 0.0066) in IUGR-pregnancies. No significance was reached when analyzing urine-Nitrite/Nitrate (P=0.7).

CONCLUSION

Whereas in preeclampsia a reduced urinary nitrite/nitrate was analyzed, IUGR pregnancies showed reduced plasma nitrite/nitrate and cGMP. A reduced release of NO into the maternal circulation might lead to the presented findings and be involved in the pathogenesis of preeclampsia and fetal IUGR.