Umbilical Artery Velocity Waveforms Research Articles

“Early Screening Test for High Risk Pregnancies by Second Trimester Color Doppler Imaging Of the Feto-Placental Circulation”

Objective: To examine the diagnostic value of umbilical artery velocity waveforms for the early detection of pregnancy induced hypertension and fetal growth restriction. To determine the utility of color Doppler Sonography of the fetoplacetal circulation for early detection of high risk pregnancies. Methods: This prospective study was conducted in the Department of Obstetrics & Gynecology, Sir Sallimullah Medical Collage & Mitford Hospital Dhaka in collaboration with radiology and imaging department of Dhaka hospital in 1st July, 2006 to 30 June, 2008. 126 randomly selected patients from 17-35 years of ages whose umbilical artery Doppler sonography was done between 16-22 weeks of gestation. All the patient were taken umbilical artery Doppler ultrasonography. Informed consent was taken from all patients. Results: A total 126 subjects of 16 to 22 weeks of gestation were included in this series. On application of the student‘t’ test for S/D ratio between normal and abnormal waveforms of the umbilical artery was found significant difference (P<.0001). Distribution of patient according to umbilical artery systolic / diastolic ratio (n=126). Normal UA waveform 76 (60%), abnormal UA waveform 50(40%), Age (Mean ±SD) in year, normal UA waveform 25.63 ± 4.47 and abnormal UA waveform 25.86±3.75. Para: Primiparous normal UA waveform 36 (60%) & abnormal UA waveform 24 (40%), multiparous normal UA waveform 40 (60.6%) & abnormal UA waveform 26 (39.4%). Gestation age at scan in weeks (Mean± SD), normal UA waveform 19.5 ±2.5, abnormal UA waveform 19±2.0. Gestation age at delivery in weeks (Mean± SD), normal UA waveform 39.03±1.61, abnormal UA waveform 35.78 ±1.53, P value 0.0001. Birth wt. in Kg. (Mean ±SD), normal UA waveform 3.10 ±0.38, abnormal UA waveform 2.42 ±0.53, P value 0.0001. S/D ratio (Mean ±SD), normal UA waveform 2.40 ±0.31, abnormal UA waveform 5.46±1.62, P value 0.0001. Cases with an abnormal outcome in relation to whether the umbilical artery waveform was classified as normal or abnormal (n=126). Abnormal outcome in PIH normal UA waveform (n=76) 4%, PIH abnormal UA waveform (n=50) 14%, P value 0.001. In PIH/FGR, normal UA waveform (n=76) 1% & abnormal UA waveform (n=50) 5%, P value 0.024. FGR normal UA waveform (n=76) 5% & abnormal UA waveform (n=50) 13%, P value 0.002. Asphyxia normal UA waveform (n=76) 0% & abnormal UA waveform (n=50) 3%, P value 0.017. PIH /IUD normal UA waveform (n=76) 0% & abnormal UA waveform (n=50) 1%. A significant association was found when the Chi Square (X 2) test was used to examine the relationship between umbilical artery blood flow and the outcome of patient (i.e FGR, PIH, fetal asphyxia). The screening test had a sensitivity of 78.26% & specificity of 82.5% and accuracy 80.95%. The predictive value of a positive test was 72% and of a negative test 86.84%. Conclusion : A close linear relationship between diagnosis of high risk pregnancy & umbilical artery Doppler velocity waveforms was observed .As umbilical artery Doppler is easy to perform and it is done in between 16 to 22 weeks of gestation can be done along with anomaly scan which is also done at 20-22 week of gestation. So, UA Doppler does not cause additional USG scan. Along with anomaly scan UA Doppler will help to screen out high risk pregnancy.

Interpretation of Wave Reflections in the Umbilical Arterial Segment of the Feto-Placental Circulation: Computational Modeling of the Feto-Placental Arterial Tree.

Placental vascular abnormalities are associated with a host of pregnancy complications including placenta mediated fetal growth restriction (FGR). Umbilical arterial (UA) Doppler ultrasound velocity waveforms are widely used in the diagnosis of underlying placental vascular abnormalities in pregnancies with suspected FGR, which greatly helps to prevent stillbirth via ongoing fetal monitoring and timely delivery. However, the sensitivity of UA Doppler diagnosis diminishes late in gestation. Our goal was to present a generalized wave decomposition method to compute forward and reflected components from UA waveforms. A detailed anatomical based model was also developed to explain observed UA flow waveform and to explore how vascular properties affect the shape of flow wave components. Using data from a previous study of pregnant mice using high frequency ultrasound microscopy, we examined in utero Doppler and M-mode ultrasound measurements in 15 fetuses' UA. Following ultrasound, the placentas had been collected and perfused with contrast agent to obtain high-resolution 3D images of the feto-placental arteries. Model of these specimens indicates the significant role of terminal load impedance (capillary and/or veins) in creating positive or negative reflected flow waveforms. A negative flow reflected waveform is obtained when terminal impedance is elevated. This is consistent with the elongated and non-branching terminal villi that are proposed to cause the highly abnormal UA waveforms found in early-onset FGR. The significance of these findings for the diagnostic utility of UA Doppler in human pregnancy is that the identification and measurement of wave reflections may aid in discriminating between healthy and abnormal placental vasculature in pregnancies with suspected late-onset FGR.

Human umbilical and fetal cerebral blood flow velocity waveforms following maternal glucose loading: a cross-sectional observational study.

Our aim was to study umbilical and fetal cerebral arterial blood flow velocity waveforms related to fetal biometric measures and maternal body mass index, glucose levels and parity following maternal oral glucose loading. The study had an experimental design in a cross-sectional observational study including 105 low-risk pregnancies (30-32weeks of gestation). Ultrasound Doppler measurements of umbilical and middle cerebral arterial (UA and MCA) velocity waveforms were performed before and at 2h after completed 75-g oral glucose tolerance tests (OGTT). We assessed changes in UA and MCA pulsatility indices (PI). MCA PI was significantly reduced following OGTT (p<0.001); these changes were not related to changes in fetal heart rate (r=-0.11, p=0.278). UA PI was also significantly reduced following OGTT (p=0.033); these changes were related to fetal heart rate (r=-0.47, p<0.001). This reduction was not significant (p=0.230) when the PI values were adjusted for fetal heart rate. The ratio MCA PI to UA PI was reduced (p=0.001). The effect of OGTT on MCA PI was not related to fetal abdominal circumference whereas the effect on the adjusted UA PI values was correlated to abdominal circumference (r=-0.20, p=0.045) but not to abdominal circumference Z-score (r=-0.16, p=0.115). The influence of OGTT on the Doppler parameters as well as heart rates was not related to prepregnant body mass index, glucose levels before or after OGTT, parity, fetal sex or gestational age. Maternal glucose loading seems to decrease fetal cerebral blood flow impedance independent of fetal size.

English

INTRODUCTION: Doppler velocimetry is a rapid noninvasive test that provides valuable information about haemodynamic situation of the foetus and is an efficient diagnostic test of foetal jeopardy which helps in timely intervention and management of high risk pregnancy for better perinatal outcome. OBJECTIVES: To evaluate middle cerebral artery and umbilical arterial velocity waveforms and their various indices during third trimester of pregnancy. METHODOLOGY: Prospective study including 50 women with normal singleton pregnancy and 50 women with intrauterine growth restricted pregnancy booked for regular antenatal checkups in our hospital. RESULTS: Foetal biometery i. e. EFW(estimated foetal weight) , BPD (bi parietal diameter), HC(head circumference), AC(abdominal circumference) and FL( femur length) all the values were significantly reduced in IUGR pregnancy. Mean amniotic fluid index was significantly reduced for IUGR pregnancy. Umbilical artery indices were significantly raised in IUGR pregnancy. Mean Pulsatility index (PI) for study group was 1.03±0.22 as compared to control group of 0.87±0.17, P value being < 0.0003. Mean Resistance index (RI) for study group was 0.65±0.14 as compared to 0.58±0.06 for control group, P value being 0.0015. Mean Systolic diastolic ratio (S/D) for study group was 2.96±0.78 as compared to 2.43±0.32 for control group, P value being < 0.0001. Reduced mean middle cerebral artery indices in IUGR pregnancy. Cerebro umbilical ratio was significantly reduced in study group. AEDV was present in 12% of women in study group and REDV in 8% women of study group. IUGR pregnancies deliver early as in comparison to normal pregnancies. Significant numbers of babies having IUGR were delivery by LSCS. Mean birth weight is significantly reduced in control for study group. Similarly, significant number of babies in IUGR pregnancies requires NICU admission .Significant number of patients in study group has associated PIH. CONCLUSIONS: In normal pregnancy there is gestational age related fall in impedance in umbilical and middle cerebral arteries. Doppler study of umbilical and middle cerebral artery is highly sensitive in the detection of IUGR and prediction of adverse perinatal outcome in small for gestational age.

Fetal Pulmonary Arterial Vascular Impedance Reflects Changes in Fetal Oxygenation at Near-Term Gestation in a Nonhuman Primate Model

We tested the hypothesis that fetal pulmonary arterial circulation reacts to changes in fetal oxygenation status at near-term gestation. A total of 20 rhesus macaques underwent fetal Doppler ultrasonography at near-term gestation. Right pulmonary artery (RPA), umbilical artery (UA), ductus arteriosus (DA), and ductus venosus (DV) blood velocity waveforms were obtained, and pulsatility index (PI) values were calculated. Fetal right and left ventricular cardiac outputs were determined. Ultrasonographic data were collected during 3 maternal oxygenation states: room air (baseline), hyperoxemia, and hypoxemia. Fetal RPA PI values increased (P < .05) during maternal hypoxemia and decreased (P < .05) during maternal hyperoxemia, compared with baseline. Maternal hyperoxemia increased (P < .05) DA PI values from baseline. Fetal cardiac outputs, UA, and DV PI values were not affected. Our results demonstrate that at near-term gestation, fetal pulmonary arterial circulation is a dynamic vascular bed that reflects acute and short-term changes in fetal oxygenation.

Three-dimensional HDlive rendering images of the TRAP sequence in the first trimester: reverse end-diastolic umbilical artery velocity in a pump twin with an adverse pregnancy outcome.

The twin reversed arterial perfusion (TRAP) sequence, also known as fetus acardius, occurs in 0.3 % of monozygotic twin gestations, which amounts to a frequency of about 1 per 35,000 deliveries [1, 2]. There have been only two reports on antenatal three-dimensional (3D) sonographic diagnosis of the TRAP sequence during pregnancy [3, 4]. The HDlive is a new surface render mode involving the use of skin-like colors, and ‘‘its system uses an adjustable light source, giving the operator the opportunity to create lighting and shadowing effects and thereby increasing depth perception’’ [5]. There have been four reports on fetal, placental, and umbilical cord ultrasound images using the 3D HDlive rendering mode [5–8]. Employing 3D HDlive with new skin-like colors, we can achieve a natural and anatomically realistic appearance of the embryo and fetus in utero. However, there has been no reports on 3D HDlive rendering displays of the TRAP sequence in the first trimester of pregnancy. There have been five reports on reverse end-diastolic velocity in umbilical artery velocimetry with an adverse pregnancy outcome at less than 14 weeks of gestation, which suggested that reverse end-diastolic umbilical artery velocity waveforms might be an ominous sign in early pregnancy [9–13]. However, there are no sonographic findings in the first trimester that can help to distinguish between pregnancies resulting in death of the pump twin from those that will survive until prophylactic intervention at 16–18 weeks in TRAP sequence cases [14]. In this report, we present our experience of a TRAP sequence reconstructed employing the 3D HDlive rendering mode, and discuss the reverse end-diastolic blood flow velocity waveform in the umbilical artery of a pump twin with an adverse pregnancy outcome in the first trimester. A 33-year-old pregnant Japanese woman, gravida 1, para 0, was referred to our ultrasound clinic because of a suspected TRAP sequence at 11 weeks and 6 days of gestation. The 2D sonography and the 3D surface rendering mode (Voluson E8, GE Healthcare, Milwaukee, WI, USA) showed a normal pump twin and small acardiac twin with acrania and absence of the heart and upper limbs (Fig. 1). The crown-rump length of the pump twin was 43.3 mm (consistent with the corresponding age), and no gross fetal anomaly was noted. The longitudinal distance between the upper pole and rump of the acardiac fetus was 27.6 mm. The 3D HDlive rendering mode provided anatomically realistic images for TRAP sequence diagnosis (Fig. 2). Color and pulsed Doppler sonography revealed a reverse end-diastolic umbilical artery velocity in the pump twin at 13 weeks and 1 day of gestation (Fig. 3a). There was a single-artery umbilical cord between the placenta and acardiac fetus, and a reversed tiny absent diastolic umbilical artery velocity was noted (Fig. 3b). Fetal demise of the pump twin was confirmed at 14 weeks’ gestation. Delivery C. Tenkumo H. Tanaka M. Ito E. Uketa N. Mori U. Hanaoka K. Kanenishi T. Hata (&) Department of Perinatology and Gynecology, Kagawa University School of Medicine, 1750-1 Ikenobe, Miki, Kagawa 761-0793, Japan e-mail: toshi28@med.kagawa-u.ac.jp

A classification of patterns of fetal middle cerebral artery velocity waveforms as seen on Doppler ultrasound

To identify, classify, and study the clinical significance of different patterns of fetal middle cerebral artery peak systolic velocity waveforms that can be seen on Doppler ultrasound. The patterns of fetal middle cerebral artery (MCA) velocity waveforms encountered in our study (n = 1128) conducted on a rural obstetric population were analyzed. Broadly, three different waveform-patterns (type I to type III) were identified from 1100 cases on which satisfactory studies were conducted. Types IA and IB were found in normal fetuses of the first (n = 254, 23.1 %) and second (n = 386, 35.1 %) trimesters, respectively. Type IC (n = 418, 38 %) included normal fetuses in the second (n = 25) and third (n = 317) trimesters, and 76 of 118 IUGR fetuses. Type II consisted of IUGR category; 17 (1.5 %) cases in type IIA, 10 (0.9 %) in IIB, and 11 (1.0 %) in IIC. Type III (n = 4, 0.4 %) was found in the critical cases with severe anemia secondary to feto-maternal hemorrhage. Although different patterns of uterine and umbilical artery velocity waveforms have been described in the obstetric literature, there is no mention of patterns of fetal MCA velocity waveforms. This is the first study to demonstrate, classify, and state the clinical significance of different patterns of fetal middle cerebral artery peak systolic velocity waveforms.

Placental ischemia and changes in umbilical and uteroplacental arterial and venous hemodynamics

Objective: To relate Doppler velocimetry findings in fetoplacental and uteroplacental circulation to placental histomorphology. Material and methods: In 14 uncomplicated and 31 high-risk pregnancies Doppler velocimetry was performed in umbilical artery and vein, and in maternal uterine veins and arteries during the second half of gestation. Histopathology of the placentas was examined, especially for signs of ischemia and inflammation. Results: All fetuses in uncomplicated pregnancies had normal flow velocity waveforms in umbilical artery; in the high-risk group, 18 fetuses had abnormal flow (increased PI or absent/reverse end-diastolic flow). The latter group had more often high ischemic score and infarctions in the placenta than found in pregnancies with normal umbilical artery flow (p < 0.001 and p = 0.02, respectively). Similarly, the abnormal uterine artery flow pattern (uterine artery score 3–4) occurred more often with high ischemic score and placenta infarctions (p < 0.001 and p < 0.001, respectively). No significant associations were found between the uterine venous flow type and placental ischemia. Conclusion: Placental ischemic morphological changes were associated with Doppler ultrasound signs of increased resistance to arterial blood flow, both on the fetal and maternal sides of the placenta. No significant relation to the uterine venous flow velocities was found.

Effect of maternal betamethasone on fetal and uteroplacental blood flow velocity waveforms

To investigate the effects of antenatal betamethasone on fetal and uteroplacental hemodynamics. The study comprised 33 women with singleton high-risk pregnancies (23-33 weeks; 27 pregnancies < 30 weeks) not in labor, but at risk for preterm delivery based on fetal or maternal indications. They were treated with two doses of 12 mg betamethasone intramuscularly 24 h apart to enhance fetal lung maturity. Flow velocity waveforms were recorded with Doppler ultrasound from the umbilical artery, the fetal middle cerebral artery, the ductus venosus and both maternal uterine arteries, once before and twice after betamethasone administration. Twenty-one (64%) women delivered within 4 days, nine (27%) women within 5-7 days and three (9%) within 8-15 days after the first dose of betamethasone. Two days after betamethasone, a decrease in pulsatility index was found in the umbilical artery (P = 0.0002) and ductus venosus (P = 0.003). Changes in the umbilical artery waveform from reversed to absent, and from absent to positive diastolic flow, were noted in 12 of 15 cases (P < 0.01). After 4 days, umbilical artery and ductus venosus velocity waveforms in the undelivered fetuses either returned to the type of waveform observed before treatment or showed further deterioration. No significant effects of betamethasone were observed in the fetal middle cerebral artery and uteroplacental circulation. Maternal antenatal betamethasone resulted in a significant transient change in the velocity waveform and a decrease in the pulsatility index in the umbilical artery and ductus venosus, but did not influence uteroplacental circulation. These findings indicate a direct effect of betamethasone on fetal circulation.

Diagnostic value of continuous wave (cw) Doppler sonography in maternal diabetes mellitus

Doppler studies of umbilical, uterine and arcuate artery velocity wave forms were performed in 40 insulin-dependent diabetic women in the first and second half of pregnancy. Using a continuous-wave Doppler device, the resistance index (RI) was calculated to determine the degree of vascular resistance in utero-placental and foeto-placental compartment. The 90th percentile was used to classify flow velocity profiles. In addition, diastolic notching and incomplete registration of uterine and arcuate arteries were considered as an abnormal result in utero-placental perfusion. The prevalence of abnormal velocity wave forms in this risk group was higher than in a non-diabetic population. No significant correlation was found between abnormal Doppler studies and White's classification. Patients with vasculopathy represent a high-risk group for foetal growth retardation, which may be detected early by umbilical and especially uterine artery Doppler studies. Abnormal uterine and arcuate artery wave forms allowed identification of patients who developed pregnancy-induced hypertension/preeclampsia.

Histomorphology of the Placenta and the Placental Bed of Growth Restricted Foetuses and Correlation with the Doppler Velocimetries of the Uterine and Umbilical Arteries

The aim of the present study was to evaluate the histomorphology of the placenta and the placental bed and to correlate this with the Doppler study of the uterine and umbilical arteries of intrauterine growth restricted pregnancies. The study group consisted of 47 women with intrauterine growth restricted foetuses. Twenty-five uneventful pregnancies with appropriate for gestational age foetuses were selected as controls. Doppler studies of umbilical and uterine arteries were performed within the last week before delivery. Placental bed biopsies were obtained at Caesarean section with direct visualization of the placental site. The incidence of pathologic bed biopsies in control, IUGR with normal uterine artery Doppler velocimetry and IUGR with abnormal uterine artery Doppler velocimetry was 0 per cent, 16.6 per cent and 79.3 per cent respectively (P< 0.001). Placentae from IUGR cases with abnormal umbilical artery Doppler velocimetries had a significantly increased number of villous infarcts, cytotrophoblast proliferation and thickening of the villous trophoblastic basal membrane (P=0.001, P=0.038 and P=0.02 respectively). Abnormal placental bed biopsy pathology was significantly associated with abnormal uterine artery velocimetry (OR 33.7, 6.5–173.6; P< 0.001). Abnormal placental pathology was significantly associated with abnormal umbilical artery Doppler velocimetry (OR 21.04, 3.8–115.9;P< 0.001). Women with both abnormal uterine and umbilical artery Doppler velocimetries were delivered earlier and their babies had lower mean birth and placental weight (P< 0.001). In conclusion, placental bed biopsy and placental pathologies are best reflected by abnormal uterine and umbilical artery velocity waveforms, respectively. The most severe clinical outcomes and perinatal mortality are present when both uterine and umbilical districts are altered.

Inactivation of the lysyl oxidase gene Lox leads to aortic aneurysms, cardiovascular dysfunction, and perinatal death in mice.

The lysyl oxidases are extracellular copper enzymes that initiate the crosslinking of collagens and elastin, 5 human isoenzymes having been characterized so far. The crosslinks formed provide the tensile strength and elastic properties for various extracellular matrices, including vascular walls. We studied the role of the first described isoenzyme Lox by inactivating its gene in mice. Murine Lox gene was disrupted by routine methods. Lox(-/-) mice died at the end of gestation or as neonates, necropsy of the live-born pups revealing large aortic aneurysms. In light microscopy, hazy and unruffled elastic lamellae in the Lox(-/-) aortas were observed, and electron microscopy of the aortic walls of the Lox(-/-) fetuses showed highly fragmented elastic fibers and discontinuity in the smooth muscle cell layers in Lox(-/-) fetuses. The wall of the aorta in the Lox(-/-) fetuses was significantly thicker, and the diameter of the aortic lumen was significantly smaller than that in the Lox(+/+) aortas. In Lox(-/-) fetuses, Doppler ultrasonography revealed increased impedance in the umbilical artery, descending aorta, and intracranial artery blood velocity waveforms, decreased mean velocities across cardiac inflow and outflow regions, and increased pulsatility in ductus venosus blood velocity waveforms. Lox has an essential role in the development and function of the cardiovascular system. Inactivation of the Lox gene causes structural alterations in the arterial walls, leading to abnormalities in the cardiovascular functions. Alterations in LOX activity may also play a critical role in certain human cardiovascular diseases.

Umbilical artery Doppler waveform notching: is it a marker for cord and placental abnormalities?

To evaluate in a prospective, controlled fashion the prevalence of umbilical artery Doppler waveform notching and its association with cord and placental abnormalities. During a 6-month period, umbilical artery velocity waveforms were prospectively obtained on 1857 pregnancies at greater than 27 weeks' gestation. All pregnant patients with the presence of a persistent fetal umbilical artery waveform notch formed the study population (cases). Control patients, matched for gestational age, with normal umbilical artery waveforms, were selected for comparison (2 controls per case). After delivery, detailed pathologic examination was performed on all umbilical cords and placentas. The presence of an umbilical artery waveform notch was noted in 29 (1.6%) of 1857 pregnancies. Postnatal placental evaluation showed the presence of an accessory placental lobe in 5 (17%) of 29 cases compared with 1 (1.8%) of 54 controls (P = .018). Overall, the presence of an umbilical artery waveform notch was associated with umbilical cord abnormalities in 21 (72%) of 29 cases compared with 8 (14%) of 54 controls (odds ratio, 15; 95% confidence interval, 4.4-54.4). Umbilical artery waveform notching appears to be a strong predictor of cord and placental abnormalities. This finding may have important clinical implications.

Outcome at school age following antenatal detection of absent or reversed end diastolic flow velocity in the umbilical artery

Aim: To determine whether fetal compromise, manifested by abnormalities of Doppler recordings of umbilical artery velocity waveforms in utero, is associated with neurodevelopmental or educational abnormalities at school age. Methods:...

Perinatal morbidity and mortality rates in severe twin-twin transfusion syndrome: Results of the International Amnioreduction Registry

Objective: Serial aggressive amnioreduction is the most widely used therapy for pregnancies that are complicated by twin-twin transfusion syndrome. Survival rates reported with this therapy are 33% to 83%, the wide range attributable to the small number of patients in these case series. Similarly, data on morbidity in survivors are imprecise. We instituted the international twin-twin transfusion syndrome registry to determine the perinatal survival and morbidity rates and the factors that influence perinatal outcome in patients with twin-twin transfusion syndrome who were treated with serial aggressive amnioreduction from 1990 to 1998. Study Design: A total of 223 sets of twins who were diagnosed with twin-twin transfusion syndrome before 28 weeks’ gestation from 20 fetal medicine referral centers were analyzed, with follow-up data until 4 weeks after birth. Results: Three hundred forty-six twins (78%; 182 recipients and 164 donors) were born alive. Two hundred sixty-six twins (60%; 144 recipients and 122 donors) were alive 4 weeks after birth. Both fetuses survived to 4 weeks in 108 pregnancies (48.4%), whereas, at least 1 fetus survived in 158 pregnancies (70.8%). The interval between the last amnioreduction and delivery ranged from zero to 138 days (median, 17.5 days). In the infants who survived to 4 weeks after birth, abnormalities on neonatal cranial scan were diagnosed in 24% of recipients and in 25% of donors. Logistic regression analysis indicated that the survival rate was significantly related to gestational age at diagnosis, presence of end-diastolic blood flow in the umbilical artery velocity waveforms, presence of hydrops, mean volume of amniotic fluid removed per week, larger birth weight, and gestational age at delivery. The hemoglobin level difference at birth was the only significant parameter to predict abnormal cranial ultrasonography in newborns. Conclusion: These data document perinatal survival and neonatal morbidity rates in severe twin-twin transfusion syndrome that were treated by serial aggressive amnioreduction. Outcome was influenced by several perinatal risk factors, which may be used to counsel patients before and during therapy. (Am J Obstet Gynecol 2001;185:708-15.)

Fetal Circulatory Responses to Maternal Blood Loss

We examined the fetal circulatory responses to maternal blood loss in pregnant women during the third trimester. Seven healthy women with placenta previa and singleton pregnancies underwent phlebotomies in an autologous donation program. Four hundred milliliters of blood was collected within 15 min at 34 and 35 weeks of gestation. Continuous electric recordings of fetal heart rate were performed during the first blood collection, and the maternal uterine artery (UtA), umbilical artery (UmA) and fetal middle cerebral artery (MCA) Doppler velocity waveforms were recorded before, immediately after and 24 h after the second collection in each patient. The average fetal heart rate, maternal UtA and UmA pulsatility indices did not change measurably during or after maternal blood collections. However, the average fetal MCA pulsatility index decreased significantly 24 h after maternal blood loss. The observation of a decrease in fetal MCA pulsatility index may indicate delayed fetal asphyxia following mild maternal hemorrhage.

Do Heart Rate and Velocity Variability Derived from Umbilical Artery Velocity Waveforms Change Prior to Clinical Pregnancy-Induced Hypertension?

Do Heart Rate and Velocity Variability Derived from Umbilical Artery Velocity Waveforms Change Prior to Clinical Pregnancy-Induced Hypertension?

Fetal Middle Cerebral Artery Doppler Waveforms in Twin–Twin Transfusion Syndrome

The aim of this study was to compare the fetal middle cerebral artery (MCA) Doppler waveforms in growth-retarded twin fetuses with (n = 11) and without (n = 24) twin–twin transfusion syndrome (TTTS). Umbilical artery (UA) and fetal MCA Doppler velocity waveforms were recorded on admission. The mean values of the UA pulsatility index (PI) of smaller twin fetuses with and without TTTS were significantly higher than those of normal singleton pregnancies. The mean values of the MCA PI of smaller twin fetuses in the TTTS group (+0.7 ± 1 SD) were significantly higher than those of normal singleton pregnancies on admission, and these levels did not markedly change following amniocentesis. On the other hand, the values of the MCA of the growth-retarded fetuses without TTTS (–0.9 ± 1 SD) were significantly lower than those of normal singleton pregnancies. Our findings suggest that measurement of fetal MCA PI is a useful method to assess growth-retarded fetuses in monochorionic twin pregnancies.

Do heart rate and velocity variability derived from umbilical artery velocity waveforms change prior to clinical pregnancy-induced hypertension?

To investigate the hypothesis that alterations in heart rate variability, peak systolic velocity variability and time-averaged velocity variability in the human umbilical artery may predict early signs of dysfunctional fetal-placental coupling in pregnancies that later develop pregnancy-induced hypertension. Doppler flow velocity recordings from the umbilical artery were performed at 10-20 weeks of gestation in 12 nulliparous women who subsequently developed pregnancy-induced hypertension. From umbilical artery velocity waveforms of at least 12 s in duration we determined absolute values and beat-to-beat variability in fetal heart rate, peak systolic and time-averaged velocity and compared these findings with those in normal nulliparous pregnant women matched for gestational age. Absolute values for fetal heart rate, peak systolic and time-averaged velocity as well as beat-to-beat variability in fetal heart rate did not differ significantly between women later developing pregnancy-induced hypertension and normal controls. However, variability in peak systolic velocity and time-averaged velocity were decreased in women who subsequently developed pregnancy-induced hypertension. Whereas fetal heart rate variability was similar, umbilical artery flow velocity variability was reduced in women developing pregnancy-induced hypertension compared with controls. It is proposed from this study that variability of the umbilical artery flow velocity is associated with mechanical changes in the vascular bed of women who later develop pregnancy-induced hypertension.

Umbilical artery flow velocity waveforms following maternal exercise

The effect of acute exercise on pregnant women in the last trimester of pregnancy and the changes in fetal umbilical artery flow velocity waveforms were studied. One hundred and forty-three healthy pregnant women underwent an acute exercise test. The exercise was performed on an upright bicycle ergometer for 5 minutes, followed by 30 minutes of recovery. The baseline control values of umbilical artery velocity waveforms were compared with those after exercise. The mean exercise intensity achieved was 67.4% (55-90%) of submaximal exercise. Maternal heart rate rose significantly from a mean of 89 (68-120) beats per minute at rest to a mean of 144 (116-200) beats per minute after exercise (P<0.001). Maternal blood pressure rose significantly after exercise from a mean systolic of 112 (80-150) mmHg to a mean of 147 (120-200) mmHg (P<0.001), and from a mean diastolic of 67 (40-85) mmHg to a mean of 84 (70-100) mm Hg (P<0.001). The mean fetal umbilical pulsatility index (PI) was shown to decrease significantly following exercise at 2 and 4 minutes of recovery. It is concluded that (1) an acute exercise test of this intensity causes a significant decrease in PI index after 2 and 4 minutes of recovery; (2) an exercise intensity between 55 and 75% causes a decrease in the PI after exercise while exercise of 76-90% of submaximal exercise causes a rebound increase after an initial decrease at 2 minutes; (3) it may be possible to use this pattern of exercise as an exercise test to differentiate between low- and high-risk pregnancies. Studies on high-risk pregnancies are being prepared for publication.