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Value of intraplacental villous artery Doppler measurements in severe preeclampsia. SS Lacin, NN Demir, FF Koyuncu, YY GoktayDepartment of Obstetrics and Gynecology and Radiology, Dokuz, Eylul University, School of Medicine, Izmir, Turkey., Turkey
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 0009715309
Blood flow velocity waveforms were recorded by color Doppler ultrasound from intraplacental villous and umbilical arteries in 20 normal and 23 severe preeclamptic pregnancies. The results of the resistance index measurements in intraplacental villous arteries were 0.51 +/- 0.037 and 0.55 +/- 0.052 in healthy controls and preeclamptics respectively, which was not significantly different. Resistance indices showed a decrease through the umbilical cord from fetus to placenta in both groups. We also noted that Doppler examination of the umbilical cord might be an early indicator of fetal compromise. Detectable intraplacental villous flows were in normal limits even in patients with abnormally high umbilical resistance indices and failure to detect villous artery color Doppler flow signals is probably associated with fetal compromise. We conclude that Doppler measurements from the intraplacental arteries cannot be used in clinical management of patients with severe preeclampsia. Keywords: Arteries, ultrasonography,Blood Flow Velocity, Case-Control Studies, Chorionic Villi, blood supply,Female, Human, Pre-Eclampsia, physiopathology,ultrasonography,Pregnancy, Reproducibility of Results, Ultrasonography, Doppler, Color, methods,Ultrasonography, Prenatal, methods,Umbilical Arteries, ultrasonography,Vascular Resistance,
The rates of preterm birth, growth retarded fetuses and perinatal death, are significantly increased in pregnancies complicated by severe preeclampsia [1],[2]. Elective preterm delivery is frequently advised for hypertensive women in an attempt to improve neonatal outcome, although this may result in higher fetal mortality and morbidity because of prematurity. Doppler ultrasound examination is a non-invasive method, which gives useful information about impaired blood flow to the fetus at risk. Previous studies in pre-eclampsia for the assessment of fetal well-being have mainly concentrated on measurements from umbilical and uterine artery[3],[4]. However, umbilical artery wave forms only reflects placental impedance to the blood flow and changes of patterns may be caused by histomorphologic alterations of the placental vascular tree. Thompson and Trudinger have shown that significant changes in the umbilical artery could not be determined before 60% of the intra-placental vasculature had occluded[5]. These results have been confirmed by experimental studies[6],[7]. Therefore, it would be logical to evaluate the primary pathological sites within the placenta. Recent technical advances with colour Doppler equipment have allowed us to examine very small intraplacental villous arteries (50-200 ?m) In this study, we tried to determine the validity of blood flow velocities in intra-placental villous arteries with colour Doppler ultrasound in patients with severe preeclampsia.
Twenty-three patients with severe preeclampsia studied at 30 to 40 weeks gestation were compared, with normal pregnant women of similar gestational ages by using Doppler indices of umbilical and intra-placental villous artery. One patient with chronic hypertension and superimposed preeclampsia and another one with insulin dependent diabetes mellitus for eight years were excluded. None of the patients were given any medication before the Doppler measurements. Also there were no other complications such as gestational diabetes, preterm birth and antepartum haemorrhage etc. Patients with severe preeclampsia were defined as those with at least one of the following criteria; diastolic blood pressure over 110 mm Hg, proteinuria more than 4 g/24h, oliguria less than 400 ml/24h persistent epigastric or subcostal pain, thrombocytopenia less than 1,00,000/ml and deterioration of liver enzymes. All patients were treated with magnesium sulfate after the Doppler evaluation and methyldopa and nifedipine were used as antihypertensive medications. Pregnancies older than 35 weeks were terminated following the Doppler measurements. We tried to prolong the pregnancies between the 30 and 35 weeks of gestation unless there was evidence of fetal and/or maternal deterioration. Maternal indications for the termination of pregnancy were uncontrolled hypertension, anuria and/or pulmonary edema, persistent thrombocytopenia and eclampsia. Fetal indications were oligohydramnios (the largest cord-free fluid pocket <1 cm vertically), spontaneous or late decelerations or markedly decreased variability on fetal heart rate tracings. Doppler measurements were repeated in one week if she had not delivered by then. Only last measurements were used in the analysis. All but two patients were evaluated according to the biophysical profile. The physicians managing the patient were not aware of the Doppler results. In the study, umbilical and intra-placental villous artery blood flow velocities were evaluated. Through the study, a Toshiba SSH-140 A colour Doppler ultrasound machine and a 3.75 MHz sector probe was used. All patients were examined in the semi lateral decubitus position following a bed rest for 10 minutes. Fetal biometric measurements were calculated using biparietal diameter, femur length and abdominal circumference. A fetus was considered as growth retarded if its estimated weight was < 10th percentile according to our national standards [8]. After determining the placental localisation and morphology, ultrasonic parameters of biophysical profile were calculated. Umbilical artery measurements were done both in a tree floating loop which is close to the fetus and in a second site which is about 2 cm away from the placental insertion. Intra-placental area was scanned and colour Doppler signals were used to facilitate the identification of the vessels. Colour resolution was maximised by narrowing the study area to a 2 x 2 cm window. At least 2 intra-placental vessels were examined except in one case in which no flow could be determined. Measurements were done after determining the fetal versus maternal arterial flow by the heart rate, and areas within the placental margin and cord insertion were not sampled. Doppler gain and flow velocity settings were changed until the maximum quality of signals were obtained. Measurements were taken during periods of inactivity and apnea, which have been shown to affect the accuracy of measurements. Insonation angle was taken less than 60 deg. and pre-systolic and end-diastolic velocities were defined manually after observing at least three consecutive waves. Each measurement was repeated twice and the average values of resistant indices were used. We noted the gestational age at delivery, incidence of caesarean delivery for fetal distress, 1st and 5th minute Apgar scores, need for neonatal resuscitation, duration of stay in neonatal intensive care unit and birth weights. Statistical analysis was performed with Mann-Whitney-U and x 2 tests within the Statistical Package For Social Sciences Software. Statistical significance was considered if p<0.05.
We found that three to five intra-placental villous arteries could be visualised and their flow patterns evaluated if carefully scanned by colour Doppler mapping system in normal cases. In severe preeclamptic group, however, we could not observe any flow in one patient, and this was one of the three IUGR cases. There was no difference in ages and parities between hypertensive and normal groups. [Table - 1] shows the perinatal outcome of the hypertensive group. The perinatal outcome of the control group was completely normal. Resistance index values in distal portion (near to the placenta) of the umbilical artery were 0.53 ? 0.053 and 0,61 ? 0.010 in control and preeclamptic group respectively (p<0.05). Values from the proximal portion (near to the fetus) of the cord were 0.63 ? 0.066 and 0.73 ? 0.086 respectively (p<0.05). The results Discussion of the measurements in intra-placental villous arteries were 0.51 ? 0.037 and 0.55 ? 0.052 in healthy controls and preeciamptics respectively which was not significantly different. Resistance indices revealed a decrease through the umbilical cord from fetus to placenta in both groups. [Figure:1] Our intra - observer variability was 7.6% for the umbilical artery and 8.2% for the intraplacental villous arteries. We did not calculate the inter -observer variation since all the measurements were done by the same examiner. When we take 0.70(+2 SD of our mean umbilical artery resistance index in the control group) as a cut-off point, it was found that there were statistically significant differences in neonatal parameters between the high and low resistance index values [Table - 2].
Non-invasive Doppler evaluation of the high-risk pregnancies is being used in most centres routinely today. Usually, however, the fetal and maternal arteries, and not the intra-placental villous arteries in severe preeclampsia have been studied. Vascular anatomy is the main component of the placental blood flow. Since the medial muscular layer and neural control of the villous blood flow do not exist, occlusive processes are responsible for the perfusion abnormalities[9]. High umbilical Doppler indices have been shown to be a measure of increased resistance in the circulation as a result of the decrease in the number of villous arteries. These findings have been supported by several studies[10],[11],[12]. In this study, the results of measurements in severe preeclamptic patients from the intra-placental villous arteries, which we considered as resistance vessels, contrary to our expectations, did not show any significant difference from the healthy population. Umbilical artery measurements, however, showed significant clinical correlation, which is consistent with the other studies [13],[14]. In one patient, no flow signal was recorded and this was one of the severe IUGR cases who died antenatally Our study was not large enough to conclude whether the absence of intra-placental colour Doppler flow signals was associated with fetal distress and/or perinatal death. We preferred the resistant index among the Doppler indices because it has the best diagnostic efficacy in predicting perinatal compromise[15],[16]. Our study was in accordance with the results of Kirkinen et al[16] concerning the downstream resistance flow gradient between the proximal and distal umbilical artery. Although we did not perform a uniform morphological placental grading, we may easily say that all the pregnancies in our control group with "aged' placentas had normal blood flow indices and normal perinatal outcomes. So, the ultrasonic morphological grading of the placenta gives little information to us about the placental function. We also noted that only 8 out of 12 fetal heart rate patterns of fetuses who had abnormal umbilical RI were ominous. Thus, Doppler examination might be an earlier indicator of fetal compromise. It was interesting that detectable intra-placental villous flows were in normal limits even in patients with abnormally high umbilical resistance indices. Doppler indices from the umbilical artery show total vascular resistance of the placental vascular bed. On the other hand, measurements from a villous merely reflects the amount of flow inside that artery itself. Here, we could assume that the occlusive pathology inside the placenta have been irregularly distributed. As the amount of occlusion of most villous arteries increases, probably others would compensate by enlarging their lumen and giving normal measurement results. This accommodation of villous arteries, which do not have muscular medial layer, provides some more blood perfusion vital to the compromised fetus. This feature that nature gives to intra-placental vessels also seems meaningful for the continuity of human being. This study showed that Doppler measurements from the intra-placental villous arteries were not as valuable as umbilical arteries in clinical management of patients with severe preeclampsia.
[Table - 1], [Table - 2]
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