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Biomedical subjects

C M Cook

Publications and source records attributed to C M Cook.

At least 55 records · Page 3Linked to original sources
PubMed1990

Umbilical artery waveforms in triplet pregnancy.

Twenty patients with triplet pregnancies underwent continuous-wave Doppler ultrasound umbilical artery waveform studies as part of a multiple-pregnancy surveillance program. One or more infants was small for gestational age in nine of these triplet pregnancies. In all of these cases, at least one abnormal umbilical artery velocity waveform was present. Two infants were stillborn, and both had a grossly abnormal umbilical artery waveform (absent diastolic flow) recorded consistently for several weeks before fetal death. The use of umbilical artery Doppler studies may delineate those triplet pregnancies in which more intensive fetal surveillance is appropriate.

Birth Weight↗
PubMed1990

Doppler umbilical artery studies in the twin-twin transfusion syndrome.

Eleven patients with twin pregnancies were identified as having twin-twin transfusion syndrome on the basis of like-sex twins with monochorionic placentation and umbilical venous blood hemoglobin differences exceeding 50 g/L at delivery. Umbilical artery velocity-time waveform studies had been performed in these pregnancies as part of a large series of 456 twin pregnancies. In all 11 cases, the systolic-diastolic (S-D) ratio differences between the twins were less than 1 unit (mean 0.4 +/- 0.2), indicating that in twin-twin transfusion, umbilical artery S-D ratios are concordant even in the presence of discordancy in fetal size.

Adult↗
PubMed1989

Fetal breathing movements--a comparison of hard copy records produced by M-mode and Doppler ultrasound.

To precisely measure the events of the fetal breath cycle it is necessary to have an accurate hard copy record. Two approaches to this have been made using either M-mode or Doppler ultrasound. It was the aim of this paper to compare these methods. Hard copy records of fetal breathing movements were produced by simultaneously recording movements of the fetal chest wall with M-mode and frequency spectral analysis of Doppler signals from either the fetal inferior vena cava or umbilical vein. Timing of the onset and end of inspiration was equally recognised by chest wall movement and changes in umbilical vein flow. Augmented flow in the fetal inferior cava began after the onset of "inspiration" and continued into "expiration". This signal could be used for registering the occurrence of a breath but not for timing. Because of unequal rotation and distortion of the chest wall, during fetal breathing movements, records of chest wall movement were considered less precise than those from the umbilical vein for timing the events of the fetal breath cycle. The umbilical vein flow velocity sonogram provides an accurate record to allow measurement of "inspiratory" time and total breath movement time.

Fetal Movement↗
PubMed1989

Reduced fetal platelet counts in pregnancies with abnormal Doppler umbilical flow waveforms.

Fetal and maternal platelet counts were correlated with antenatal assessment of the umbilical-placental waveform. Forty singleton pregnancies were studied using Doppler ultrasound, and placental resistance was categorized as normal or high according to the systolic/diastolic ratio. We performed platelet counts on maternal and cord blood taken at the time of cesarean section. The high-resistance group had a mean fetal platelet count (218 +/- 53 x 10(3)/microliters) significantly lower than that of the normal-resistance group (314 +/- 76 x 10(3)/microliters) (P less than .001). This difference was evident in both the hypertensive and nonhypertensive subgroups of the high-resistance group. There was no difference in mean maternal platelet counts between the high- and normal-resistance groups.

Adult↗
PubMed1988

Low-dose aspirin therapy improves fetal weight in umbilical placental insufficiency.

A randomized, placebo-controlled, double-blind trial was carried out to evaluate the fetal benefits of low-dose aspirin (150 mg/day) as a treatment of placental insufficiency during the last trimester of pregnancy. Forty-six women referred for study because there was concern about fetal welfare were found to have an elevated umbilical artery wave form systolic/diastolic ratio. Mothers with severe hypertension were excluded because fetal condition would not necessarily be the dominant determinant of obstetric decision making. A distinction was made between a high systolic/diastolic ratio (greater than 95th but less than 99.95th percentile) and an extreme systolic/diastolic ratio (greater than 99.95th percentile). There were 34 patients in the high ratio group and 12 in the extreme group. Aspirin therapy was associated with an increase in birth weight (mean difference 526 gm [p less than 0.02]), head circumference (1.7 cm [p less than 0.025]), and placental weight (136 gm [p less than 0.02]) in those patients with a high initial umbilical artery systolic/diastolic ratio. For the 12 women with an extreme initial systolic/diastolic ratio, aspirin therapy did not result in a significantly different pregnancy outcome.

Adult↗
PubMed1988

Umbilical artery flow velocity waveforms and twin pregnancy outcome.

Two hundred seventy-two twin pregnancies were studied by analysis of the fetal umbilical artery waveforms recorded using continuous-wave Doppler ultrasound. After the first 100 cases, a management strategy was adopted whereby all twin gestations would be studied between 28-32 weeks' gestation and the results made available to the referring obstetrician, thereby influencing clinical management. Perinatal mortality and morbidity, in pregnancies with both fetuses alive at 28 weeks' gestation, were compared between the patients studied in the first group of 100 and those studied after the Doppler examination was introduced as a clinical service. There was a decrease in perinatal mortality, both uncorrected (57.9 per 1000 to 17.9 per 1000; P less than .05) and corrected (42.1 per 1000 to 8.9 per 1000). Fetal deaths were reduced from six to one (P less than .05). This decrease in perinatal mortality was achieved without any appreciable change in the gestational age at delivery or mode of delivery between the two groups. There was a reduction in the number of infants requiring neonatal intensive care (from 38% to 24%; P less than .01).

Birth Weight↗
PubMed1988

Doppler ultrasound waveform indices: A/B ratio, pulsatility index and Pourcelot ratio.

Three different indices, the A/B ratio, the pulsatility index (PI) and the Pourcelot ratio (PR), are in common use for quantitative analysis of umbilical artery Doppler ultrasound waveforms. A detailed examination of the similarities and differences between these indices, together with the expected errors for each, was undertaken to enable informed comparisons and choices to be made. The indices were calculated from 133 last trimester recordings using an objective and very reliable computer analysis technique. The PI is more difficult to calculate than the other two quantities and the extra computation does not provide any extra information. The A/B ratio appears the simplest index to use but the values are not normally distributed. With the PR a normal distribution of values can be assumed. A theoretical consideration of errors showed that none of the indices is intrinsically less error prone for last trimester waveforms overall. The errors in the A/B ratio increase as the value of the index increase, whereas the converse holds for the PI and PR.

Blood Flow Velocity↗
PubMed1988

Umbilical artery velocity waveforms: normal reference values for A/B ratio and Pourcelot ratio.

Normal reference values for the umbilical artery Pourcelot ratio and A/B ratio are reported. Thirty-five normal patients were studied serially from 20 weeks to term. The A/B ratio centiles were corrected for non-normality of the underlying distribution by transforming from the Pourcelot ratio values. The correction needed was small during the last trimester, but larger for second trimester data. Of the 35 patients 24 were nulliparous and there was a slight tendency for the waveform indices to be higher in the nulliparae, but the numbers in this study were too small to be conclusive about the effect of parity.

Blood Flow Velocity↗
PubMed1988

Monitoring lupus anticoagulant-positive pregnancies with umbilical artery flow velocity waveforms.

The presence of the "lupus anticoagulant" in maternal blood is associated with thrombosis in the placental vessels and a high rate of fetal loss. We followed six pregnancies in four mothers positive for lupus anticoagulant autoantibody with Doppler umbilical flow studies. The women were not treated with any drugs, and clinical management was guided by close fetal surveillance including umbilical flow studies. Umbilical artery flow velocity waveforms detect vascular abnormalities in the fetal umbilical placental circulation and were used as an early indicator of developing disease. All pregnancies produced live-born infants. These cases indicate the potential value of such studies in the management of this group at high risk of fetal loss.

Autoantibodies↗
PubMed1988

Different umbilical artery flow velocity waveforms in one patient.

Serial studies of umbilical artery flow velocity waveforms in one patient revealed two quite distinct waveforms at each study. The mean systolic/diastolic ratio difference between the studies was 2.2 units. After delivery, the placenta was seen to include a large infarcted lobule supplied by only one of the umbilical arteries. The finding of two very dissimilar umbilical artery flow velocity waveforms at the time of study should raise the suspicion of placental infarction, but management decisions should be based on the most normal study.

Adult↗
PubMed1987

Umbilical artery flow velocity waveforms in high-risk pregnancy. Randomised controlled trial.

300 patients at high fetal risk (mean gestational age 34 wk) were randomised to a group for antenatal doppler umbilical artery waveform studies and a control group. The timing of delivery was similar in the control and doppler-report-available groups overall. However, in the report group obstetricians allowed the pregnancies of those not selected for elective delivery to continue longer. There was no difference in the rates for elective delivery (induction of labour or caesarean section) in the two groups, whereas among those who went into labour (induced or spontaneous) emergency caesarean section was more frequent in the control group (23%) than in the report group (13%). Fetal distress in labour was also more common in the control group. Babies from the control group spent longer in neonatal intensive care (level 3) and needed more respiratory support than did those in the report group. The findings indicate that the availability of doppler studies leads to better obstetrical decision making.

Blood Flow Velocity↗
PubMed1986

A comparison of Doppler ultrasound waveform indices in the umbilical artery--I. Indices derived from the maximum velocity waveform.

Various Doppler waveform indices have been used for assessment of the fetal circulation. Comparisons were made to show what relations exist between the indices, and to identify any differences or difficulties which might arise from using one as opposed to another in clinical practice. Both normal pregnancy and cases of fetal growth failure were studied. Indices were obtained from the maximum velocity envelope of the umbilical artery waveform using a curve fitting technique. The values were very reproducible for all indices. The FHR, which varied over the entire normal range, did not significantly affect the values of any index. The downstream impedance indices calculated included the AB ratio, pulsatility index (PI) and Pourcelot ratio. These all gave very closely correlated results for normals but discrepancies occurred in the at risk group, where values were elevated. This could be attributed to differences in the underlying distributions. The indices suggested for cardiac contractility were not as closely related to each other, and moreover the differences between them showed no clear pattern. None of the indices varied independently of the others. The rising slope, which is by definition related to the PI, was more highly correlated with the downstream indices than the relative flow rate index.

Blood Flow Velocity↗
PubMed1986

A comparison of Doppler ultrasound waveform indices in the umbilical artery--II. Indices derived from the mean velocity and first moment waveforms.

Umbilical artery Doppler recordings in both normal pregnancy and cases of fetal growth failure were processed by computer. Representative waveforms for the maximum velocity, mean velocity and first moment were obtained after ensemble averaging and correction for thump filtering. The same set of indices, which included the AB ratio, pulsatility index, rising slope and relative flow rate index, were calculated for each of the waveforms. The results were compared to identify differences which might arise in clinical practice if a waveform other than the usual (maximum velocity) was used. The ratio of the mean to the maximum velocity, which gives an indication of the velocity profile, was shown to be very error prone. The reproducibility of the mean velocity and first moment indices was inferior to that of the maximum velocity indices. The results from the different waveforms were highly correlated for normals for most indices. However, in the growth retarded group there was a tendency for the mean velocity and first moment indices to classify as normal studies classified as abnormal by the maximum velocity index. The values of indices derived from the first moment waveform were generally larger than the maximum and mean velocity values. For the relative flow rate index, where results were often different to the general trend, the values were more nearly equal.

Blood Flow Velocity↗