Warwick B. Giles

Fetal umbilical artery flow velocity waveforms and placental resistance: pathological correlation

Summary. Placental microvascular anatomy was correlated with antenatal assessment of the umbilical circulation in 106 patients to further validate the measurement of the A/B ratio (the ratio of peak systolic to least diastolic flow velocity) of the umbilical artery flow velocity time wave‐forms as an index of blood flow resistance. Three groups of patients were studied: a normal group of 38 uncomplicated pregnancies, a control group of 33 potentially ‘at risk’ pregnancies with a normal A/B ratio matched by risk factors and gestation with the third group of 35 pregnancies with a high A/B ratio. Placental arterial resistance was quantitated by counting the number of small muscular arteries (<90 μm diameter) in the tertiary stem villi in a standard microscopic field (mean 18·5 fields/placenta). The modal small arterial vessel count was shown to be significantly less in the group with a high fetal risk and a high A/B ratio (1–2 arteries/field) than in both the normal and control groups (7–8 arteries/field). The tertiary villus count did not vary between groups. Antenatal studies of umbilical artery flow velocity waveforms with Doppler ultrasound identify a specific microvascular lesion in the placenta characterized by obliteration of small muscular arteries in the tertiary stem villi.

Fetal umbilical artery flow velocity waveforms and placental resistance: clinical significance

Summary. Since the umbilical arteries carry fetal blood to the placenta we studied flow velocity waveforms in these vessels with a simple continuous wave Doppler system to assess placental blood flow. The ratio of peak systolic to least diastolic (A/B) flow velocity was measured as an index of placental flow resistance. In 15 normal pregnancies there was a small but significant decrease in this ratio through the last trimester. The A/B ratio was measured on 436 occasions in 168 high‐risk pregnancies. In 32 of 43 fetuses subsequently shown to be small for gestational age there was an increase in placental flow resistance with reduced, absent or even reversed flow in diastole. This finding was also present in the one fetus which died in utero. Serial studies in patients with fetal compromise indicated increasing flow resistance, a reverse of the normal trend. These results were not available to the clinician yet of 24 fetuses born before 32 weeks 13 had a high A/B ratio, and all of them were born electively. Maternal hypertension was associated with an increase in fetal placental flow resistance. The umbilical artery A/B ratio provides a new and non‐invasive measure of fetoplacental blood flow resistance.

Uteroplacental blood flow velocity-time waveforms in normal and complicated pregnancy.

Summary. A simple continuous wave Doppler ultrasound system for recording arterial flow velocity waveforms in branches of the uterine artery in the placental bed is described. Twelve normal pregnancies were studied serially from 20 weeks to delivery. The diastolic flow velocity expressed as a percentage of the systolic provides an index of downstream vascular bed resistance and perfusion. This always exceeded 50% in normal pregnancy and there was a small increase with gestational age indicative of a decreasing flow resistance. Of the 91 complicated pregnancies, studied because of potential uteroplacental insufficiency and fetal risk, 25 resulted in the birth of an infant small‐for‐gestational‐age. In 15 the uterine artery flow velocity waveform revealed a pattern of low diastolic flow velocity. It is postulated that these represent a subgroup of growth‐retarded fetuses in whom there is reduced uterine artery perfusion. Reduced uterine artery diastolic flow velocity in these patients was associated with reduced umbilical artery diastolic flow velocity on the fetal side of the placenta. In contrast the 10 small‐for‐gestation infants associated with normal uterine artery waveforms suggest a primary fetal cause. Twelve patients with severe hypertensive disease of pregnancy were studied. Nine were associated with reduced uterine artery diastolic flow velocity (reduced uterine artery perfusion) consistent with vasospasm in the branches of the uterine artery in the placental bed.

A comparison of fetal heart rate monitoring and umbilical artery waveforms in the recognition of fetal compromise

Summary. Antenatal fetal heart rate monitoring was compared with the study of umbilical artery flow velocity waveforms for the recognition of fetal compromise in 170 patients considered at high fetal risk. In 53 patients the infant had a 5‐min Apgar score of <7 and/or a birthweight < the 10th centile of weight for gestation. Fetal heart rate traces were classified as reactive or non‐reactive and also assessed with a modified Fischer score. The systolic/diastolic A/B ratio was measured in the umbilical artery waveform. Fetal compromise was more efficiently recognized by study of the umbilical artery waveforms. The sensitivity of assessment by umbilical artery waveforms was 60% compared with 17% and 36% respectively, for the two methods of scoring fetal heart rate traces. This was not associated with an increase in false‐positive results as the predictive value of both positive (64% compared with 69 and 58%) and negative (83% compared with 72 and 75%) results was similar when umbilical artery waveform analysis was compared with the two methods of scoring fetal heart rate traces. Specificity was also similar (85% compared with 97 and 88%).

Fetal umbilical artery flow velocity‐time waveforms in twin pregnancies

Summary. The umbilical artery flow velocity‐time waveforms were studied in 76 twin pregnancies. The ratio of peak systolic (A) to least diastolic (El) velocity was calculated for each fetus as an index of umbilical placental flow resistance. Seventy‐one sets of twins were studied within 14 days before delivery. In 65 cases both twins were alive at the time of study. In 32 pregnancies both fetuses were of birthweight appropriate for gestational age (AGA) and had A/B ratios within the normal singleton range. In 33 pregnancies one or both of the liveborn infants were small for gestational age (SGA) and in 78% of these at least one fetus had an elevated A/B ratio. Discordancy in birthweight and A/B ratio was associated with growth retardation. Clinically manifest twin‐to‐twin transfusions occurred in five of the ten pregnancies resulting in an SGA infant (eight with discordant weight) associated with a normal and concordant A/B ratio. Two twin‐to‐twin transfusions were associated with perinatal death. The placentas were examined in 61 patients. In 43 dichorionic pairs the A/B ratio was elevated in 12 of the 18 where there was at least one SGA infant. There was a greater incidence of growth retardation in the monochorionic pairs (12 of 18). Only seven of these were identified by an elevated A/B ratio. In 10 of these 18 pairs vascular anastomoses were demonstrated on placental inspection and in a further two there was evidence of twin‐to‐twin transfusion by haemoglobin discrepancy. Twin pregnancy may result in the birth of a small‐for‐dates infant because of intrauterine growth retardation or twin‐to‐twin transfusion. An abnormally elevated A/B ratio identifies growth retardation. In twin‐to‐twin transfusion the A/B ratio of the two fetuses is similar (crossed circulation) yet difference in size may be seen on ultrasound measurement.

The effect of epidural anaesthesia for caesarean section on maternal uterine and fetal umbilical artery blood flow velocity waveforms

Summary. The blood flow resistance in the maternal uteroplacental and fetal umbilical artery circulation was studied in eight otherwise normal patients undergoing elective lower segment caesarean section. The systolic/diastolic A/B ratio (the ratio of peak systolic to least diastolic flow velocity) for the uteroplacental and fetal umbilical circulation was determined from the artery blood flow velocity‐time waveform and used as an index of blood flow resistance. Each patient received a 1 litre intravenous crystalloid infusion before an epidural bupivicaine injection. Both crystalloid infusion and epidural anaesthesia resulted in a significant decrease in the maternal uteroplacental systolic/diastolic (A/B) ratios, associated with a decrease in fetal umbilical artery A/B ratio. This study suggests a beneficial fetal effect from the improved maternal uterine perfusion after epidural anaesthesia.

Umbilical cord whole blood viscosity and the umbilical artery flow velocity time waveforms: a correlation

Summary. The possibility was examined of an association between umbilical cord whole blood viscosity and umbilical artery flow velocity time waveforms obtained with continuous wave Doppler ultrasound. The cord blood viscosity was measured at both high (100 s‐l) and low (0·1 s‐I) shear rates with a concentric cylinder viscometer. Plasma viscosity and fibrinogen were also measured. An abnormal pattern in the umbilical artery flow velocity waveform (high A/B ratio) indicative of high resistance was associated with an increase in whole blood viscosity at high shear (which may reflect a change in red cell rigidity). Viscosity at low shear (reflecting red cell aggregation and rouleaux formation) did not differ. There was a significant association between the small‐for‐gestational age fetus and abnormal umbilical artery waveform study (P <0·002) but not abnormal whole blood viscosity at high (P=0·09) or low (P=0·08) shear.

Teenage Pregnancy in Western Sydney

Summary: The obstetric performance of 121 young teenagers (less than 17 years of age) confining as public patients at Blacktown District Hospital was retrospectively compared with a randomly‐selected control group of older gravidas. These adolescents were less likely to be married, to be certain of their last menstrual period, to book into the hospital early or to attend the antenatal clinic regularly than their older counterparts. However, there was no difference in the rates of anaemia, spontaneous or operative delivery, gestational age at confinement, birth‐weight, perinatal mortality or neonatal morbidity rates. When the teenagers were compared with primigravidas from the control group, labour length was significantly shorter and the rates of preeclampsia were similar. These results are more optimistic than previous overseas reports regarding the obstetric performance of young adolescents.

Trauma during pregnancy--a review of management

Summary: The assessment and management of 22 pregnant patients who were admitted after trauma to Westmead Hospital between July, 1987 and October, 1988 was reviewed. Thirteen of the 22 patients were victims of motor vehicle accidents. Despite the fact that an injury research unit, responsible for the clerking and review of all trauma patients, is well established at our institution, only 6 patients in this series had been assessed in this fashion. Although a number of important obstetric investigations (albeit uncommon in the accident and emergency room situation) are well described in the literature, these were not performed in a number of patients. A protocol for the management of such patients is recommended so that more standardized and appropriate care might be given to the injured pregnant patient.

Elaboration of stem villous vessels in growth restricted pregnancies with abnormal umbilical artery Doppler waveforms

counselling should differ accordingly, but few clinicians appear to tailor the information they give: of 15 post-membership obstetricians we surveyed, none were aware of the lower detection rate in younger women. We suggest that the main benefit of serum screening is not that it can be applied to women of all ages but that it gives an option for women of 35 years or more to avoid invasive testing (and miscarriage of a normal fetus).