Phasic blood flow patterns in the common umbilical vein of fetal sheep during umbilical cord occlusion and the influence of autonomic nervous system blockade

The blood flow pattern in the common umbilical vein is under normal conditions nonpulsatile in contrast to the flow in the fetal inferior vena cava. We observed pulsatile flow patterns in the common umbilical vein of fetal lambs during changes in the fetal hemodynamic equilibrium. These pulsations may influence the mixing of oxygen-rich ductus venosus blood and oxygen-poor inferior vena cava blood. This study deals with the phasic changes in umbilical venous blood flow during cord occlusion. The experiments were performed in eight chronically instrumented fetal lambs between 114 and 133 days gestation (term 146 days). Umbilical venous blood flow was measured with an electromagnetic flow transducer around the intraabdominal common part of both umbilical veins. The fetuses were provided with catheter in the fetal abdominal aorta and with electrodes for monitoring arterial blood pressure and heart rate. Occlusion of the umbilical cord was performed by means of an inflatable balloon occluder around the total cord (occlusion time 20 to 90 seconds). Occlusions were performed in fetuses with an intact autonomic nervous system and after blockade of the alpha-adrenergic, beta-adrenergic or cholinergic part of the autonomic nervous system.     

Effects of maternal oxygen administration on fetal oxygenation during reductions in umbilical blood flow in fetal lambs

In 11 chronically catheterized fetal lambs (123 +/- 6, mean +/- SD, days of gestation; term = 147 days), we measured fetal oxygen delivery and oxygen consumption before and during reductions in umbilical blood flow (Qumb). Qumb was reduced by inflation of a balloon occluder located just proximal to the origin of the common umbilical artery. Measurements were made while the unanesthetized maternal sheep received either room air or 100% oxygen to breathe. In oxygen-treated fetuses, oxygen concentrations in umbilical venous blood (Cuvo2) and arterial blood (Cao2) were increased over a wide range of Qumb when compared with those of room air-treated fetuses. Because of these responses, fetal oxygen delivery (Do2 = Qumb X Cuvo2) and oxygen consumption [Vo2 = Qumb(Cuvo2-Cao2)] were greater in oxygen-treated fetuses than in room air-treated fetuses during episodes of reduced Qumb. In oxygen-treated fetuses, Vo2 decreased from normal levels only when Qumb was less than or equal to 75 ml/min/kg of fetus, whereas in room air-treated fetuses Vo2 decreased at Qumb less than or equal to 150 ml/min/kg. Our data indicate that oxygen administration to the pregnant sheep increases oxygen delivery to the fetus during times of reduced umbilical perfusion and that this supplemental oxygen supply provides an oxygen reserve with which the fetus can maintain oxidative metabolism. These data may be relevant to those clinical conditions, such as umbilical cord compression in labor, that are associated with reductions in umbilical blood flow.     

Simultaneous measurements of umbilical venous, fetal hepatic, and ductus venosus blood flow in growth-restricted human fetuses

OBJECTIVE: The purpose of this study was to evaluate the changes in the distribution of the umbilical venous blood flow to the liver and to the ductus venosus in intrauterine growth-restricted human fetuses in relationship with dilation of the ductal isthmic diameter. STUDY DESIGN: Umbilical venous flow, ductus venosus blood flow, and blood flow to the fetal liver were measured in 56 severely intrauterine growth-restricted fetuses with an abnormal pulsatility index of the umbilical artery and were compared with 137 normal control fetuses. Percentages of umbilical venous blood flow through the ductus venosus and to the fetal hepatic lobes were calculated. Z-scores for control fetuses and intrauterine growth-restricted fetuses were constructed by the evaluation of the inverted smoothed percentiles. The distributions of the Z-scores was compared with a 1-sample t-test. RESULTS: The ductus venosus blood flow that was corrected for fetal weight was increased significantly in intrauterine growth-restricted fetuses compared with control fetuses (P=0); the median values (interquartile range) for comparable ages of gestation was 41.3 mL/min/kg (range, 26.2-64.0 mL/min/kg) and 30.8 mL/min/kg (range, 19.9-42.8 mL/min/kg), respectively. As a consequence, ductus venosus shunting was increased in intrauterine growth-restricted fetuses compared with control fetuses (P =0). In 23 of 30 intrauterine growth-restricted fetuses, the percentage of umbilical blood flow that was shunted through the ductus was>90th percentile of control fetuses. Ductal diameters were significantly greater in growth-restricted fetuses than in control fetuses (P =.0001). The percentage of blood flow to the right lobe showed a significant reduction (P =.0223), with evidence of reversed blood flow from the right lobe and portal system into the ductus venosus that was provided both by volume blood flow calculations and by direct pulsed Doppler waveform direction. CONCLUSION: In severe intrauterine growth-restricted fetuses, Doppler examination of blood flow volume proved a significant increase in the shunting of umbilical vein blood flow through the ductus venosus that was associated with the dilation of the ductal isthmic diameter. These changes provide a relatively constant blood flow to the heart and brain at the expense of fetal hepatic perfusion.     

Effect of repetitive umbilical cord occlusions on neuronal brain activity measured by the cerebral function analyzing monitor and histologic outcome in immature fetal sheep

OBJECTIVE: To examine the effect of repetitive total umbilical cord occlusions on electrocortical brain activity as measured by cerebral function analyzing monitoring (CAFM) and the histologic outcome in immature sheep fetuses. STUDY DESIGN: We performed brief repeated total umbilical cord occlusions, two every 5 minutes, in 12 immature sheep fetuses (at 90 days of gestation, term 147 days) until fetal mean arterial pressure dropped below 50% of baseline value during two successive occlusions. A pair of electrodes was inserted on the parietal dura for recording of electrocortical brain activity (ECoG). Off-line ECoG signal processing consisted of amplitude integrated analysis (CFAM) and spectral analysis. Fetal blood gas analyses were performed at regular intervals just before subsequent umbilical cord occlusions. Three days after the occlusion neuronal damage was evaluated histologically in three regions of the fetal brain. RESULTS: CFAM amplitide parameters decreased significantly during the first occlusion and remained so during the entire repetitive occlusion period (analysis of variance [ANOVA]; P <.05). Spectral analysis of the ECoG signal demonstrated no changes in the distribution of frequency bands. Progressive acidemia and hypotension developed with ongoing occlusions. Five fetuses died at the end or shortly after the entire repetitive occlusion period. No neuronal damage or macroscopic intraventricular and/or germinal matrix hemorrhage was observed in the surviving fetuses. CONCLUSION: Repetitive umbilical cord occlusions in immature sheep fetuses resulted in functional, not structural changes of the fetal brain in surviving fetuses. At this gestational age, amplitude analysis is more sensitive than spectral analysis of the ECoG signal to functional changes of the compromised fetal brain.     

Effects of cytomegalovirus infection in pregnant women to fetuses: study with DNA-DNA hybridization method]

DNA of cytomegalovirus (CMV) was examined in 131 placentae and 28 umbilical blood specimens by DNA-DNA hybridization. The result revealed that CMV DNA was detected in 4 of 50 placentae from abnormal fetuses (31 fetal deaths, 19 fetal deformities). 77 placentae from normal fetuses showed negative results. One of 2 cord blood samples from fetal deformities showed CMV DNA positive. 25 umbilical blood samples from normal term newborns showed negative. 4 placentae and 1 cord blood sample from premature infants showed negative results. The results indicate that CMV may play a great role in fetal death and fetal deformity through the infected maternal-fetal circulation.     

Depression of uterine blood flow during total umbilical cord occlusion in sheep

The effect of total umbilical cord occlusion upon maternal blood flow in the internal iliac and median uterine arteries was studied in eight chronically instrumented pregnant sheep. Occlusion of the umbilical cord was performed with an inflatable balloon occluder around the total cord. Blood flow was measured with electromagnetic flow transducers. Total umbilical cord occlusion of short duration (mean 40.1 s) caused a significant decrease in blood flow in the maternal internal iliac and median uterine arteries at the end of the occlusion to respectively 93.9% and 91.7% of the control values.The decrease in internal iliac and median uterine artery blood flow is attributed to an elevated fetal capillary pressure in the placenta, leading to an increased fetal placental tissue pressure which in turn compresses the maternal placental capillaries, resulting in a heightened vascular resistance and a decrease in uterine blood flow.     

Omphalocele and umbilical cord cyst. Prenatal diagnosis

We present a case of intrauterine fetal death at 32 week's gestation with omphalocele, umbilical cord allantoic cyst and polyhydramnios. Ultrasound diagnosis of anomalies was performed at 23 weeks of gestation. Fetal karyotype was normal: 46 XX. This association has been found to have a high rate of chromosomal abnormalities, especially trisomy 18. It's difficult to explain the reason why intrauterine fetal death has happened; one possible hypothesis is that the cord cyst, compressing umbilical vessels, have caused intrauterine vascular compromise of blood flow.     

Single umbilical artery: prenatal findings

In 450 patients with pregnancy at high risk for fetal malformation and/or intrauterine growth retardation, the umbilical cord was investigated sonographically for the presence of a single umbilical artery. A single umbilical artery was diagnosed in four fetuses between 23 and 33 weeks of gestation and suspected in two. Three cases were overlooked at sonography. All seven surviving fetuses had growth retardation at delivery and four also showed severe malformations. Whenever a single umbilical artery is found at sonography, further work-up is required to rule out associated anomalies, intrauterine growth retardation, or chromosomal abnormality.     

Umbilical cord knots

BACKGROUND: Umbilical cord knots may represent a hazard to the fetus, particularly as regards intrauterine death and fetal distress or asphyxia in labor. The object of this study was to analyze the impact of associated umbilical cord encirclements and cord length on fetal outcome and fetal weight deviation. METHODS: Among 22,012 births occurring in Akershus Central Hospital, there were 216 instances of umbilical cord knots. Fetal outcome, fetal weight deviation, associated umbilical cord encirclements and cord length were assessed. RESULTS: Neonates with a knotted cord are more often large-for-gestational age compared to other babies, and have longer umbilical cords. There is a 10 times higher chance of intrauterine fetal death with a knotted cord, but if this does not occur then there is no increased risk of obstetrical intervention and Apgar scores are the same as in other babies and other fetuses. CONCLUSION: There is an association between umbilical cord knots and umbilical cord encirclements. Knotting of the cord is not by itself lethal. Pregnancies with knotted cords have characteristics different from those with ordinary umbilical cord encirclements.     

V-shaped deceleration differs in the pattern of carotid blood flow from variable deceleration provoked by cord compression

OBJECTIVE: To investigate whether V-shaped decelerations in fetal heart rate tracing are a physiologic response to fetal movements or secondary to cord compression. STUDY DESIGN: Six pregnant sheep and their fetuses (115-125 days of gestation) were surgically instrumented and studied. Fetal electrocardiogram, carotid blood flow, arterial blood pressure and fetal movement were continuously monitored for 24 hours. Following the undisturbed 24 hour recording, these parameters were monitored during umbilical cord compression (n = 6). Differences in these parameters between V-shaped decelerations and decelerations provoked by cord compressions were examined. RESULTS: Elevation of blood pressure and decreased carotid blood flow were observed coincidentally with the initiation of V-shaped decelerations. In cord compression, elevation of both blood pressure and carotid blood flow were followed by a decreased heart rate. V-shaped decelerations exhibited a different alteration of carotid blood flow compared to decelerations caused by umbilical cord compression. CONCLUSION: V-shaped deceleration is a physiologic response secondary mainly to fetal movements and is not caused by cord compression.     

Direct determination of the ovine fetal umbilical artery blood flow waveform

Ultrasonographic umbilical artery blood flow velocity waveform analysis has been proposed as a means of noninvasive assessment of fetal well-being. We computed waveform indices from directly measured umbilical artery blood flow in chronically instrumented ovine fetuses from 109 to 138 days of gestation (term, 145 days). The three waveform indices (systolic/diastolic ratio, pulsatility index, and resistance index) correlated significantly with each other (r = 0.90 to 0.98). These indices progressively decreased with gestation and were significantly correlated with calculated umbilical vascular resistance (r = 0.68 to 0.70, p less than 0.01) and with umbilical blood flow (r = -0.71, p less than 0.01). During the final week of pregnancy, systolic/diastolic ratio could be predicted by the combination of placental size (total cotyledonary mass), fetal size (ponderal index), and either umbilical blood flow or umbilical vascular resistance (multiple linear regression, r2 = 0.94). Fetal heart rate declined from day 109 of gestation to 138 days. Fetal heart rate was significantly correlated with waveform indices only when values exceeded 170 beats/min (r = -0.37 to -0.51). Ovine fetal umbilical artery waveform indices changed at approximately the same rate as those reported for human fetuses in late gestation on the basis of external Doppler ultrasonographic velocity measurements. These results suggest that the sheep is a suitable model for investigations of umbilical artery waveform analysis.     

Ten-minute umbilical cord occlusion markedly reduces cerebral blood flow and heat production in fetal sheep

OBJECTIVE: The study was undertaken to determine to what extent a 10-minute total umbilical cord occlusion affects autoregulation of cerebral blood flow and cerebral heat production in the fetus. STUDY DESIGN: In seven chronically catheterized late-gestation fetal sheep (127-131 days' gestation), we studied fetal blood gas, hemodynamic, and thermal responses to 10-minute total umbilical cord occlusion. RESULTS: Ten-minute umbilical cord occlusion resulted in marked hypoxia/ischemia, with oxygen content decreasing from 6.5 +/- 0.4 to 0.6 +/- 0.1 vol% and lactate concentration increasing from 1.8 +/- 0.2 to 10.7 +/- 0.7 mmol/L. During this period, the fetuses showed reductions in heart rate from 163.5 +/- 3.4 to 97.1 +/- 5.4 beats/min, mean arterial pressure from 39.4 +/- 2.1 to 21.2 +/- 2.5 mm Hg, cerebral blood flow from 101.3% +/- 8.9% to 49.7% +/- 10.3%, and cerebral heat production from 95.0% +/- 6.3% to 29.6% +/- 4.8%. During cord occlusion, cerebral blood flow was pressure passive from the fourth minute onward. The reduction in cerebral heat production preceded the reduction in perfusion pressure and cerebral blood flow. Recovery of cerebral blood flow and heat production to control values was incomplete for more than 60 minutes after restoration of umbilical flow. CONCLUSION: Ten-minute total umbilical cord occlusion results in major reductions in cerebral blood flow and heat production. Autoregulation of cerebral blood flow was lost within 4 minutes of occlusion, probably as a result of hypoxia, combined with hypotension. The fact that the reduction in cerebral heat production preceded and exceeded the reduction in blood flow may suggest active down-regulation of cerebral metabolism, the mechanism of which is unclear at present.     

Decreasing maternal nutrient intake during the final third of pregnancy in previously overnourished adolescent sheep: effects on maternal nutrient partitioning and feto-placental development

When pregnant adolescent sheep are overnourished during pregnancy normal nutrient partitioning priorities to the gravid uterus are altered, leading to impaired placental development and fetal growth restriction. We hypothesized that decreasing dietary intake in overnourished dams during the final third of gestation may reverse this inappropriate nutrient partitioning in favor of the fetus. Adolescent ewes were offered control (C; n?=?12) or high (H; n?=?20) dietary intakes to induce normal vs. compromised placental development. Ten ewes receiving the H intake were switched to a low intake at d90 of gestation (HL). Between d90 to 130, HL dams lost weight and adiposity, and metabolic hormones and glucose at d130 were less than H and similar to C. In spite of these maternal changes, at d130 fetal bodyweight was equivalent in HL and H groups and ～20% less than in C. A greater degree of brain sparing was evident in HL fetuses and glucose and insulin concentrations were more perturbed than in H fetuses. Relative to C, placentome weight was reduced by 46 and 32% in H and HL and the fetal:placentome weight ratio was H?>?HL?>?C. Placental vascular morphology was largely unaffected by maternal diet during late gestation but mRNA expression of five angiogenic genes was up-regulated in the fetal cotyledon of HL pregnancies, commensurate with blood vessel remodeling. Nevertheless, overfeeding to promote maternal anabolic growth during adolescent pregnancy impairs feto-placental development that cannot be rescued by reducing maternal intake during the final third of gestation.     

Perinatal adaptive response of the adrenal and carotid blood flow in sheep fetuses subjected to total cord occlusion.

OBJECTIVE: To investigate the perinatal adaptive response of the adrenal blood flow/adrenal fractional moving blood volume (AFMBV) and carotid blood flow (CBF), in sheep fetuses subjected to severe acute intrauterine hypoxia/asphyxia induced by total cord occlusion. METHODS: Adrenal blood flow velocity, AFMBV and CBF were measured in 13 exteriorized fetal sheep; eight of them underwent total umbilical cord occlusion to induce severe acute hypoxia/asphyxia. Five lambs were used as sham controls. Middle adrenal artery pulsatility index (MAAPI) and mean velocity (MAAMV) were recorded with pulsed Doppler ultrasound. AFMBV was estimated using power Doppler ultrasound. CBF was recorded with a transonic flowmeter. In the neonatal period, after resuscitation all lambs were followed for a 4-hour period and AFMBV and CBF were recorded. Mean arterial blood pressure (MABP) and fetal heart rate were recorded continuously. Arterial cortisol levels were measured at the beginning and at the end of the fetal and neonatal periods. RESULTS: Following the total cord occlusion, there was a significant reduction in the CBF, MABP, and heart rate and adrenal flow/AFMBV after 2, 4 and 5 min, respectively. Cortisol levels in the asphyctic lambs at the end of the cord occlusion were significantly lower than those in controls. After resuscitation, the asphyctic lambs showed increased AFMBV and cortisol levels, and reduced MABP as compared to control lambs. No differences were found in CBF, MAAPI and MAAMV. Thereafter, no differences were observed between the two groups in any of the studied parameters. At the end of the cord occlusion period, there was a significant correlation between AFMBV and MABP (r=0.69), between AFMBV and CBF (r =0.65) and between CBF and MABP (r=0.89). CONCLUSION: During severe acute intrauterine hypoxia, the fetal lamb is able to maintain the blood flow to the brain and the adrenal gland for 3-5 min. Changes in the AFMBV and the CBF were highly correlated to the changes in MABP. Adrenal FMBV and cortisol levels were higher in lamb neonates exposed to severe intrauterine asphyxia.     

Relationship of umbilical vein blood flow to growth parameters in the human fetus.

OBJECTIVE: Our purposes were to determine the relationship of the growth of umbilical blood flow to growth in body measurements of human fetuses in uncomplicated pregnancies. The study also aimed to assess the relative contributions of growth in umbilical vein diameter and of increased velocity to the increase in umbilical blood flow. STUDY DESIGN: An animal study was conducted to assess the accuracy of umbilical vein blood flow measurements obtained by triplex mode ultrasonography. Seven pregnant ewes underwent triplex mode umbilical vein flow determination. These results were compared with historical flow data obtained by a steady-state diffusion technique in 34 ewes matched for gestational age and weight. In a separate study performed on human beings, reproducibility and precision of triplex mode flow determination were assessed, as were the relationships between umbilical vein flow and gestational age and head and abdominal circumferences. This cross-sectional study was performed with 70 healthy fetuses ranging from 20 weeks' gestation to term. Best-fit interpolating equations and confidence limits were calculated for blood flow measurements versus gestational age and head and abdominal circumferences. RESULTS: In the validation study performed on sheep there were no significant differences between triplex mode and steady-state measurement groups with respect to gestational age or weight. The umbilical vein flows were similar between triplex mode and steady-state measurement groups (P =.881). In the human study the intraobserver and interobserver coefficients of variation for the vein diameter, mean velocity, and absolute umbilical vein blood flow varied from 2.9% to 12.7%. The mean duration of examination was 3 +/- 1 minutes. The umbilical vein diameter and mean velocity increased throughout pregnancy. The absolute umbilical vein flow increased exponentially from 97.3 mL/min at midgestation to 529.1 mL/min at 38 weeks' gestation, whereas umbilical vein flow per kilogram of fetal weight did not change significantly with gestational age. There was a strong correlation between absolute umbilical vein flow and the fetal head and abdominal circumferences. CONCLUSIONS: The triplex mode ultrasonographic technique can play an innovative role in obtaining quick and reproducible measurements of umbilical vein blood flow. The approach was validated with a sheep model. Umbilical vein blood normalized for fetal weight (milliliters per minute per kilogram of fetal weight) and absolute flow (in milliliters per minute) are consistent with previous human studies. We have established new reference values of umbilical vein blood flow relative to head and abdominal circumferences. The growth of umbilical venous diameter accounted for most of the growth in umbilical vein flow.     

Umbilical vein blood flow in rhesus-isoimmunization

In 18 pregnancies complicated by rhesus-isoimmunization, blood flow in the fetal umbilical vein was measured by a noninvasive technique combining real-time and pulsed Doppler ultrasound. Blood flow was found to be elevated in severely affected fetuses and immediately after intrauterine blood transfusion. Blood flow in the fetal umbilical vein was inversely correlated with cord haemoglobin concentration at birth (r = -0.68). The technique used can be used for noninvasive assessment of fetal condition in rhesus-isoimmunization.     

Histo-morphology of the uterus and early placenta of the African buffalo (Syncerus caffer) and comparative placentome morphology of the African buffalo and cattle (Bos taurus)

Differences exist in reproductive physiology between African buffalo (Syncerus caffer), cattle (Bos taurus) and water buffalo (Bubalus bubalis). The aim of this study was to histo-morphologically compare the anatomy of non-pregnant and pregnant uteri of buffalo and cattle. Two non-pregnant uteri and placentae of six pregnant African buffalo were used. Early placentome formation (fetal crown rump length (CRL): 2-17.5 cm) in S. caffer and B. taurus was compared. The endometrium of buffalo uteri comprises round to ovoid, dome-shaped and gland-free caruncles. A predominantly simple columnar epithelium of non-ciliated cells covers caruncular tissue, while, additionally, ciliated cells occur in the epithelium of the intercaruncular areas and within the simple columnar or pseudostratified epithelium of the endometrial glands. During early gestation, multiple placentomes develop. Unlike the placentomes in cattle at similar CRL, buffalo placentomes do not develop a caruncular stalk. The sessile, dome-shaped buffalo placentome has simple, slightly conical villi branching less than in cattle, thus indicating different and less complex feto-maternal interdigitation than seen in the latter. A synepitheliochorial interhaemal barrier can be expected in the buffalo placenta, as the occurrence and ultrastructure of trophoblast giant cells resemble those described in cattle.     

Umbilical vein blood flow in rhesus-isoimmunization

Summary. In 18 pregnancies complicated by rhesus-isoimmunization, blood flow in the fetal umbilical vein was measured by a noninvasive technique combining real-time and pulsed Doppler ultrasound. Blood flow was found to be elevated in severely affected fetuses and immediately after intrauterine blood transfusion. Blood flow in the fetal umbilical vein was inversely correlated with cord haemoglobin concentration at birth ( r =−0.68). The technique used can be used for noninvasive assessment of fetal condition in rhesus-isoimmunization.     

Early and persistent reduction in umbilical vein blood flow in the growth-restricted fetus: a longitudinal study

OBJECTIVE: We have previously shown, in a cross-sectional study, that the reduction in umbilical vein blood flow in intrauterine growth-restricted fetuses is due to reduced umbilical vein velocity. The purpose of this longitudinal study in intrauterine growth-restricted fetuses was to determine whether the umbilical vein velocity reduction, which, in turn, reduces blood flow, persists throughout gestation or represents a late event that precedes indicated delivery. STUDY DESIGN: Twenty-one intrauterine growth-restricted fetuses with an abnormal umbilical artery velocimetry underwent serial sonographic and Doppler examinations from 23 to 36 weeks of gestation. Umbilical vein diameter and velocity were measured, and umbilical vein absolute (milliliters per minute) and weight-specific blood flow (milliliters per minute per kilogram) were calculated. Umbilical vein diameter, velocity, and blood flow were expressed per abdominal circumference. Intrauterine growth-restricted findings were compared to local reference data. RESULTS: Intrauterine growth-restricted fetuses showed persistent reductions in umbilical vein blood flow per abdominal circumference and weight-specific blood flow (milliliters per minute per kilogram) from the time of diagnosis of intrauterine growth-restriction. Umbilical vein velocity was reduced in the intrauterine growth-restricted fetuses, although umbilical vein diameter did not change. CONCLUSION: Reduction of umbilical vein blood flow is an early finding in intrauterine growth-restricted fetuses, and it can persist for several weeks until delivery. This reduction in blood flow is due to reduced umbilical vein velocity.     

Intravenous pancuronium bromide for fetal neuromuscular blockade during intrauterine transfusion for red-cell alloimmunization

Intravenous pancuronium bromide was administered into the umbilical cord by funipuncture to effect temporary fetal paralysis. Neuromuscular blockade was achieved in 12 fetuses undergoing a total of 34 intrauterine procedures for the treatment of severe red-cell alloimmunization. The same initial dose of 0.2 mg/kg fetal weight estimated by ultrasound was used in all cases, but anemic fetuses did not resume movement for prolonged periods. A relationship among fetal hematocrit, adjusted dose, and duration of paralysis was described by the equation: Duration (hours) = 5.24 + 10.30 adjusted dose (mg/kg) - 0.16 hematocrit (%) (R2 = 0.49; P less than .001). Intravenous pancuronium was found to be a safe and effective method for cessation of fetal movement during intrauterine procedures.