A longitudinal study of umbilical artery Doppler waveforms in normal pregnancy: analysis using Laplace transform techniques

Objective To analyse umbilical artery Doppler waveforms using the Laplace transform analysis technique, an alternative method of waveform shape analysis, and to determine the normal ranges for the variables of this technique throughout normal pregnancy.
Design A prospective longitudinal study.
Setting Department of Obstetrics and Gynaecology, Nottingham University Hospital.
Sample A cohort of 17 healthy women investigated every four weeks from the end of the first trimester until term.
Methods Umbilical artery Doppler signals were recorded and analysed using the Laplace transform analysis technique. The median and interquartile ranges for each variable were determined and serial changes during pregnancy described.
Results Vessel wall tone decreases in the umbilical artery at the beginning of the second trimester. Alpha, the variable related to upstream flow conditions, also decreases at this stage of pregnancy but values are then comparatively stable from 24 weeks of gestation until term. A fall in downstream resistance within the fetoplacental circulation during pregnancy is detected using the C-coefficient. Real pole appears to be of no value in the assessment of downstream resistance to flow in the fetus.
Conclusions The normal ranges for the Laplace transform analysis variables have been established for the umbilical artery longitudinally through normal pregnancy. Changes in fetal blood flow during complicated pregnancy can now be investigated using this technique.     

The maternal cerebral circulation in pre-eclampsia: investigations using Laplace transform analysis of Doppler waveforms

Objective To compare the maternal cerebral circulation in pre-eclampsia and normal pregnancy using an alternative method of Doppler waveform analysis called the Laplace transform analysis, which provides haemodynamic data additional to standard Doppler indices.
Design A prospective cross-sectional study.
Setting Department of Obstetrics and Gynaecology, Nottingham University Hospital.
Sample The study involved 17 women in the third trimester of a normal pregnancy, 11 with pregnancyinduced hypertension and 26 with pre-eclampsia.
Methods Doppler recordings were obtained from the internal and external carotid and middle cerebral arteries, with the measurements in hypertensive women being carried out before any treatment was given. The waveforms were then subjected to Laplace transform analysis which provides information on vessel wall stiffness and upstream and downstream flow conditions.
Main outcome measures The determination of the Laplace transform analysis parameters, including alpha, the natural frequency of oscillation and real pole, and pulsatility index.
Results Laplace transform analysis demonstrated a significant increase in vessel wall stiffness in all the arteries in hypertensive pregnancies, but this was more marked in pre-eclampsia. The data were also consistent with, but do not prove, increased downstream resistance in the middle cerebral artery in women with pre-eclampsia but not in those with pregnancy-induced hypertension.
Conclusions The Laplace transform analysis of Doppler waveforms yields important physiological information concerning the cerebral circulation in pre-eclampsia, not detected using conventional Doppler indices. The results suggest that both pre-eclampsia and pregnancy-induced hypertension are associated with increased cerebral arterial wall stiffness and that, in addition, there may be cerebral vasoconstriction in pre-eclampsia.     

Fetal and maternal Doppler flow velocity waveforms in normal sheep pregnancy

Abnormalities in placental vascular resistance have been shown to have an important association with intrauterine growth retardation in both human and sheep pregnancies. In this study we have assessed impedance to blood flow through the ovine placental circulation by Doppler flow velocity waveform analysis. As gestation advanced from 66 to 136 days, a significant decrease in impedance to flow was observed in both umbilical and maternal placental arteries. The greatest decrease in impedance was observed between 66 and 109 days' gestation in umbilical arteries and between 66 and 80 days' gestation in maternal placental arteries. In these normal pregnancies, no significant correlations could be found between Doppler flow velocity waveform analyses and fetal or placental growth. We conclude that Doppler flow velocity waveform analysis is a valuable and non-invasive method to assess impedance to blood flow through the placental circulation in pregnant sheep.     

A longitudinal study of platelet behaviour and thromboxane production in whole blood in normal pregnancy and the puerperium

A longitudinal study of platelet behaviour (platelet aggregation and release reaction) in whole blood and of serum thromboxane B2 production was performed before, during and after normal pregnancy. The response of platelets to arachidonic acid and to adrenaline was significantly increased in the third trimester. Six weeks after delivery, values were still modestly increased but return to non-pregnant values was complete by 12 weeks. Serum thromboxane B2 production was unchanged throughout pregnancy and the puerperium.     

A longitudinal study of platelet behaviour and thromboxane production in whole blood in normal pregnancy and the puerperium

Summary. A longitudinal study of platelet behaviour (platelet aggregation and release reaction) in whole blood and of serum thromboxane B₂ production was performed before, during and after normal pregnancy. The response of platelets to arachidonic acid and to adrenaline was significantly increased in the third trimester. Six weeks after delivery, values were still modestly increased but return to non-pregnant values was complete by 12 weeks. Serum thromboxane B₂ production was unchanged throughout pregnancy and the puerperium.     

Blood flow velocity waveforms in large maternal and uterine vessels throughout pregnancy and postpartum: a longitudinal study using Duplex sonography

Blood flow velocity waveforms in large maternal and uterine vessels were measured longitudinally from 16 weeks gestation onwards until 12 weeks postpartum in 21 singleton pregnancies by duplex sonography. In the maternal carotid artery, time average mean velocity (TAVmean) did not show significant changes. In both the femoral artery and vein, however, significant changes were observed. In the femoral artery, TAVmean and systolic maximum velocities decreased with advancing gestation. In the femoral vein, TAVmean remained constant throughout pregnancy and was lower than postpartum. The resistance index in the uterine arteries decreased with advancing gestation and increased after delivery. Among many factors contributing to femoral arterial blood flow velocity changes in pregnancy, we suggest that a major one is the increase in uterine blood flow. Reduction in venous femoral blood flow velocity and increase in the femoral vein diameter might be associated with the common occurrence of venous disorders in pregnancy.     

Blood flow velocity waveforms in large maternal and uterine vessels throughout pregnancy and postpartum: a longitudinal study using Duplex sonography

Summary. Blood flow velocity waveforms in large maternal and uterine vessels were measured longitudinally from 16 weeks gestation onwards until 12 weeks postpartum in 21 singleton pregnancies by duplex sonography. In the maternal carotid artery, time average mean velocity (TAVmean) did not show significant changes. In both the femoral artery and vein, however, significant changes were observed. In the femoral artery, TAVmean and systolic maximum velocities decreased with advancing gestation. In the femoral vein, TAVmean remained constant throughout pregnancy and was lower than postpartum. The resistance index in the uterine arteries decreased with advancing gestation and increased after delivery. Among many factors contributing to femoral arterial blood flow velocity changes in pregnancy, we suggest that a major one is the increase in uterine blood flow. Reduction in venous femoral blood flow velocity and increase in the femoral vein diameter might be associated with the common occurrence of venous disorders in pregnancy.     

Fetal blood velocity waveforms in normal pregnancies. A longitudinal study

Blood velocity in the umbilical artery, fetal descending aorta and fetal middle cerebral artery was recorded by means of 3.5 MHz pulsed Doppler ultrasound in 22 normal pregnancies. The measurements were performed longitudinally between 25 and 42 weeks of gestation. The maximum blood velocity curves were analysed for pulsatility index (PI), systolic/diastolic velocity ratio (S/D ratio) and in the middle cerebral artery also for the resistance index according to Pourcelot (RI). In the umbilical artery, all variables decreased significantly with increasing gestational age as an expression of the decreasing placental vascular resistance. PI in the descending aorta remained fairly constant during the examined period of gestation. In the middle cerebral artery, all three variables (PI, S/D ratio, RI) decreased significantly as gestation advanced. With the exception of the umbilical artery at 28-32 weeks, PI and S/D ratio were not influenced by the heart rate in any of the vessels examined. Diagrams of the gestational age-related reference values (means +/- 2 SD) for the variables of the blood velocity waveforms were established. Additionally, a ratio of the PI and S/D was calculated for the umbilical artery and middle cerebral artery.     

Stroke and minute distance in pregnancy: a longitudinal study using Doppler ultrasound

Using Doppler ultrasound directed at the aortic arch, stroke and minute distance were measured in 45 normal singleton pregnancies and compared with 42 controls. In the non-pregnant controls, stroke distance was 5% more in the supine than in the left lateral position (P less than 0.01) and during pregnancy this relativity was maintained until 36 weeks gestation. In the supine and left lateral positions respectively, stroke distance was increased by 8% (both) at 4 weeks (P less than 0.05 and NS), by 14 and 11% at 8 weeks (P less than 0.001 and P less than 0.01) and showed a maximum increase of 21 and 20% at 16 weeks gestation (both P less than 0.001). At 40 weeks, supine stroke distance was 14% less than the non-pregnant control value (P less than 0.001), and 6% less than the value in the left lateral position (P less than 0.05), which was itself not significantly different from that in the non-pregnant controls. The maximum increase of heart rate was at 32 weeks, by 24% in the supine and by 19% in the left lateral position (both P less than 0.001). Minute distance was maximally increased by 37% in the supine at 16 weeks (P less than 0.001) and by 30% in the left lateral position at 24 weeks (P less than 0.001). Thereafter, minute distance, measured in both positions, declined until at 40 weeks it was not significantly different from the non-pregnant control value.     

Continuous wave Doppler flow velocity waveforms from the umbilical artery in normal pregnancy

The objective was to establish a normal reference range of the indices of umbilical artery waveforms using continuous wave doppler ultrasound. A prospective longitudinal study was made of 85 uncomplicated singleton pregnancies between 16 and 40 weeks gestation (783 recordings). Pulsatility Index (P.I.), Resistance Index (R.I.) and A/B ratio were measured at each visit. The mothers all delivered normal healthy infants weighing more than the 10th centile for gestational age. All three indices have a positively skewed frequency distribution, a factor not generally appreciated until recently and the ranges are therefore described using non-parametric statistics. Placental resistance decreases as term approaches, the 50% PI at 16 weeks was 2.06, at 32 weeks was 1.08 and at 40 weeks was 0.85. The results show a comprehensive reference of normal values and provides a sound basis for the further study of abnormal pregnancy. It represents the largest published study of its type using continuous wave Doppler.     

A longitudinal study using ultrasound to assess flow-mediated dilatation in normal human pregnancy.

OBJECTIVE: To develop normal ranges of endothelial function in normal human pregnancy to use as a screening test for preeclampsia. METHODS: In this longitudinal study, women were studied five times during pregnancy and once postpartum using flow-mediated dilatation (FMD). FMD is a noninvasive ultrasound technique used to assess endothelial function. Healthy nonpregnant women were controls. RESULTS: FMD increased non-significantly in pregnancy until 32 weeks, when it decreased significantly at 36+ weeks (n = 47). CONCLUSION: The fall in FMD in the third trimester has not been previously reported. This indicates the importance of gestational age when assessing FMD as a screening test for preeclampsia.     

A longitudinal study of serum adiponectin during normal pregnancy

Adiponectin is secreted from adipose tissue. Serum adiponectin levels are inversely correlated with body mass index (BMI) and also insulin resistance, independent of the BMI. A role for adiponectin in the development of insulin resistance has been implied in pregnancy. However, no studies have been performed to describe the individual longitudinal course of adiponectin in normal pregnancies. Therefore, we measured serum adiponectin during and after normal pregnancy in 11 healthy women. Serum levels peaked in midpregnancy and the lowest levels were seen in late pregnancy. An inverse association with maternal BMI was observed.     

Doppler ultrasound of the maternal uterine arteries: disappearance of abnormal waveforms and relation to birthweight and pregnancy outcome

BACKGROUND: To assess whether the gestation at which abnormal uterine artery waveforms disappear is related to birthweight and complications of pregnancy. METHODS: A prospective study of outcome of pregnancy after a uterine artery Doppler screening program set in an inner city teaching hospital. One thousand five hundred and twenty-four consecutive women attending the Obstetric Department for a routine anomaly scan at between 19 and 21 weeks gestation had maternal uterine arteries assessed using color wave Doppler. Those women in whom the flow was deemed abnormal were recalled for a further scan at 24-26 weeks gestation. The main outcome measures were birthweight, gestation at delivery and incidence of pre eclampsia. RESULTS: The women in whom the uterine artery blood flow was normal at 20 weeks had babies with significantly higher mean birthweight than those who normalized between 20 and 24-26 weeks gestation ('late normalizers') after adjustment for confounding factors; gestational age, maternal height, parity, ethnic group and smoking (mean difference=173 g, 95% confidence intervals 42 to 303 g). CONCLUSIONS: The timing of trophoblast invasion, as reflected by abnormal uterine artery waveforms, may have an effect on birthweight.     

Maternal cerebral Doppler velocimetry before, during, and after a normal pregnancy: a longitudinal study

OBJECTIVE: Our purpose was to determine normative data for maternal cerebral blood flow indices. Study design. A prospective longitudinal study. METHODS: The maternal middle cerebral artery was examined by transcranial Doppler ultrasound in 14 healthy women before (0-10 months prior to conception) and during pregnancy (at 8, 15, 22, 29, and 36 weeks of gestation), and twice after delivery (at 8 and 24 weeks). Middle cerebral artery blood flow velocities were recorded, and pulsatility index and cerebral perfusion pressure were calculated. RESULTS AND CONCLUSION: Pulsatility index of middle cerebral artery peaked in mid-pregnancy and was constantly increased between 8 and 29 weeks of gestation. The diastolic middle cerebral artery velocity remained fairly constant at about 40 cm/s during the study period, while the systolic velocity peaked at 15 weeks (mean 102 cm/s). Cerebral perfusion pressure dropped to its lowest levels in mid-pregnancy and after delivery.     

Uterine and ovarian flow velocity waveforms in the normal menstrual cycle: a transvaginal Doppler study

A combined transvaginal 2D real-time and pulsed Doppler method was used for recording flow velocity waveforms in the uterine and ovarian arteries from 16 healthy women during the follicular and luteal phase of the normal menstrual cycle. Continuous forward end-diastolic flow velocities were documented in 74% of the ovarian artery and 96.5% of the uterine artery flow velocity waveforms. Comparison of the pulsatility index from the left and right ovarian artery revealed a significantly lower pulsatility index on the side of the ovary bearing the developing corpus luteum, suggesting reduced down-stream impedance or increased blood flow. The pulsatility index from the uterine artery only seems to be marginally involved in the observed impedance changes during the luteal phase of the menstrual cycle.     

Longitudinal study of plasma lipids and lipoprotein cholesterol in normal pregnancy and puerperium

Plasma lipids and lipoprotein cholesterol distribution were measured in 60 normal pregnancies studied longitudinally at 12, 20, 28, and 36 weeks of gestation and 3 and 40 days postpartum. Total cholesterol, unesterified cholesterol, phospholipids, triglycerides and cholesterol in low- and very-low-density lipoproteins rose progressively during pregnancy. Maximal values were reached at 36 weeks for total cholesterol, unesterified cholesterol and low-density lipoprotein cholesterol and at partum for triglycerides, very-low-density lipoprotein cholesterol and phospholipids. High-density lipoprotein cholesterol was hardly affected by pregnancy. During the second half of pregnancy and postpartum period, high-density lipoprotein cholesterol was consistently and negatively correlated with triglycerides and very-low-density lipoprotein cholesterol. In each period studied total cholesterol showed very high positive correlation with low-density lipoprotein cholesterol but a weak correlation with high-density lipoprotein cholesterol.