Changes in uterine blood flow during uterine contractions

During spontaneous and oxytocin-induced labor, recordings were made of relative uterine blood flow (thermistor method), intrauterine pressure, femoral venous and arterial pressures, and maternal heart rate. In prelabor, uterine blood flow exhibits frequent irregular waves quite independent of the observed uterine activity. During labor there is a characteristic relationship between uterine blood flow and uterine contractions. An initial decline in uterine blood flow precedes the contraction by about half a minute, followed by partial or complete recovery in the early contractile phase. A second drop begins as the intrauterine pressure reaches about 30 mm. Hg, and the decline continues to the peak of the contraction or beyond. After the contraction is completed, the uterine blood flow recovers to its original level.     

Doppler assessment of the renal blood flow velocity waveform during indomethacin therapy for preterm labor and polyhydramnios

To investigate the effects of indomethacin on the human fetal renal blood flow velocity waveform, 17 fetuses whose mothers were treated for preterm labor (N = 8) or polyhydramnios (N = 9) were studied. There were five growth-retarded fetuses (all in the group with polyhydramnios), 11 normal fetuses, and one fetus with red-cell alloimmunization. The indomethacin dose in all patients was 25 mg orally every 6 hours. The gestational age of the fetuses studied varied between 24-35 weeks (mean +/- SD 29.6 +/- 2.8). The fetal renal artery was studied at its origin from the aorta before and during the first 24 hours of indomethacin therapy. Seven fetuses manifested ductal constriction. Three fetuses also manifested tricuspid regurgitation. All ductal constrictions and the tricuspid regurgitations resolved in utero after discontinuation of indomethacin. There were no significant differences in the pulsatility index values of the renal artery before and during indomethacin therapy. These results suggest that there is no change in fetal renovascular parameters detectable with pulsatility index measurements during the first 24 hours of maternal indomethacin therapy.     

Changes in uterine blood flow during human pregnancy

A transvaginal duplex Doppler ultrasonography system was used to measure blood flow characteristics in the ascending uterine artery before and during pregnancy. The system uses a 5 MHz Doppler transducer coupled to a 6.5 MHz imaging probe. There was a steady increase in volume flow rate in the left ascending uterine artery from a mean of 94.5 ml/min before pregnancy to a mean of 342 ml/min in late gestation (reflecting a 3.5-fold increase). With the assumption of equal flow on both uterine arteries, the fraction of the cardiac output that is distributed to these vessels was calculated to be 3.5% in early pregnancy and to reach 12% near term. The mean diameter of this vessel in the nonpregnant state was 1.6 mm, increasing to 3.7 mm toward term. The resistance to flow, expressed as the peak systolic to end-diastolic flow velocity ratio, declined from a mean of 5.3 in the nonpregnant state to a mean of 2.3 near term. These changes reflect the perpetual growth and development of the uteroplacental circulation, which provides the metabolic demands of the growing fetus throughout gestation.     

Ultrasonography and blood flow velocity waveform assessment in human fetuses.

The authors report their experience with the use of ultrasonography and fetal blood flow measurement in the evaluation of fetal conditions recording patients with previous repeated immunologic abortion (R.I.A.) and with pre-eclampsia. In both groups of patients, the two biophysical methods, proved to be extremely valuable indicators of the fetal conditions.     

Daily variability of umbilical and lateral uterine wall artery blood velocity waveform measurements

Summary. The daily variability of umbilical artery and lateral uterine wall artery velocity-time waveforms recorded by continuous wave Doppler ultrasound was determined by making three observations in each of 97 women on different days within a 7-day period. There were no significant changes in the maximal:minimal Doppler shift frequency (A/B ratio) or the pulsatility index in either artery over the period of study. Common pregnancy complications did not influence the variability of the recordings. The variability of uterine artery recordings was not affected by gestational age between 17 and 41 weeks but the degree of variability of the umbilical artery recordings was greater before 30 weeks. We conclude that after 30 weeks gestation this technique has an acceptable range of daily variability for clinical and research applications.     

Daily variability of umbilical and lateral uterine wall artery blood velocity waveform measurements

The daily variability of umbilical artery and lateral uterine wall artery velocity-time waveforms recorded by continuous wave Doppler ultrasound was determined by making three observations in each of 97 women on different days within a 7-day period. There were no significant changes in the maximal:minimal Doppler shift frequency (A/B ratio) or the pulsatility index in either artery over the period of study. Common pregnancy complications did not influence the variability of the recordings. The variability of uterine artery recordings was not affected by gestational age between 17 and 41 weeks but the degree of variability of the umbilical artery recordings was greater before 30 weeks. We conclude that after 30 weeks gestation this technique has an acceptable range of daily variability for clinical and research applications.     

Fetal volume blood flow and umbilical artery flow velocity waveform analysis: a comparison

Summary. The estimation of fetal umbilical vein and aortic volume blood flow was compared with umbilical artery flow velocity-time waveform analysis in 42 pregnancies. The volume blood flow measurements were made with a combined linear array B-mode and pulsed Doppler ultrasound system. The umbilical artery flow velocity-time waveform analysis was made with either pulsed or continuous wave 2 MH_zDoppler ultrasound and the systolic/diastolic (A/B) ratio was used as an index of flow resistance. There was no difference when continuous wave was compared to pulsed Doppler ultrasound as a method of recording flow velocity waveforms. Analysis of the umbilical artery flow velocity-time waveform was more sensitive (100%-50%) than the measurement of umbilical vein volume blood flow (ml/kg/min) in the detection of the small-for-gestational age (SGA) fetus. The predictive value of a positive test was higher (71%-45%) while specificity was similar (88%-81%). Descending aortic volume flow was reduced in only one SGA fetus. The increase in umbilical placental downstream resistance (high systolic/ diastolic ratio) was associated with a reduction in the percentage of fetal aortic blood flow directed to the umbilical placental circulation.     

Fetal volume blood flow and umbilical artery flow velocity waveform analysis: a comparison

The estimation of fetal umbilical vein and aortic volume blood flow was compared with umbilical artery flow velocity-time waveform analysis in 42 pregnancies. The volume blood flow measurements were made with a combined linear array B-mode and pulsed Doppler ultrasound system. The umbilical artery flow velocity-time waveform analysis was made with either pulsed or continuous wave 2 MHz Doppler ultrasound and the systolic/diastolic (A/B) ratio was used as an index of flow resistance. There was no difference when continuous wave was compared to pulsed Doppler ultrasound as a method of recording flow velocity waveforms. Analysis of the umbilical artery flow velocity-time waveform was more sensitive (100%-50%) than the measurement of umbilical vein volume blood flow (ml/kg/min) in the detection of the small-for-gestational age (SGA) fetus. The predictive value of a positive test was higher (71%-45%) while specificity was similar (88%-81%). Descending aortic volume flow was reduced in only one SGA fetus. The increase in umbilical placental downstream resistance (high systolic/diastolic ratio) was associated with a reduction in the percentage of fetal aortic blood flow directed to the umbilical placental circulation.     

Renal arterial blood flow velocity waveforms in pregnant women

Seventy-two continuous-wave Doppler ultrasonographic examinations were performed on nine nonpregnant and 56 normal pregnant women. The range of gestation was 6 to 40 weeks, and the objective was to record the renal arterial blood flow velocity waveform. Acceleration time and systolic per diastolic ratio of renal arterial blood flow velocity waveforms were assessed. Of 72 examinations, 68 recordings were made of the left renal artery (94.4%) and 28 of the right renal artery (38.9%), respectively. There was no correlation between acceleration time and systolic per diastolic ratio and gestational age, respectively, and no correlation between acceleration time and systolic per diastolic ratio, and caliceal diameter of the renal pelvis, respectively. Acceleration times of the left and right renal arteries were 47 +/- 11 and 40 +/- 8 msec in nonpregnant women and 62 +/- 23 and 62 +/- 23 msec in pregnant women, respectively. The left and right systolic per diastolic ratios were 3.1 +/- 0.7 and 2.9 +/- 0.5 in nonpregnant women and 2.8 +/- 0.6 and 2.6 +/- 0.5 in pregnant women, respectively. Therefore these data provide a foundation for the study of hydronephrosis, which may occur in pregnant women.     

Fetal volume blood flow and umbilical artery flow velocity waveform analysis: a comparison

Summary. The estimation of fetal umbilical vein and aortic volume blood flow was compared with umbilical artery flow velocity-time waveform analysis in 42 pregnancies. The volume blood flow measurements were made with a combined linear array B-mode and pulsed Doppler ultrasound system. The umbilical artery flow velocity-time waveform analysis was made with either pulsed or continuous wave 2 MH_zDoppler ultrasound and the systolic/diastolic (A/B) ratio was used as an index of flow resistance. There was no difference when continuous wave was compared to pulsed Doppler ultrasound as a method of recording flow velocity waveforms. Analysis of the umbilical artery flow velocity-time waveform was more sensitive (100%-50%) than the measurement of umbilical vein volume blood flow (ml/kg/min) in the detection of the small-for-gestational age (SGA) fetus. The predictive value of a positive test was higher (71%-45%) while specificity was similar (88%-81%). Descending aortic volume flow was reduced in only one SGA fetus. The increase in umbilical placental downstream resistance (high systolic/ diastolic ratio) was associated with a reduction in the percentage of fetal aortic blood flow directed to the umbilical placental circulation.     

Relationship between fetal heart rate and umbilical blood flow velocity in term human fetuses during labor

Fourteen pregnant women between 37 and 41 weeks' gestational age, who subsequently were delivered of healthy newborn infants, were studied to examine the effects of spontaneous changes in fetal heart rate on the flow-velocity waveforms in the umbilical artery. The women were in active labor and under epidural anesthesia at the time Doppler measurements were made. There was a significant positive relationship between end-diastolic flow velocity and fetal heart rate. The umbilical artery peak-systolic/end-diastolic ratio was best correlated with the negative reciprocal transformation of the instantaneous fetal heart rate value and end-diastolic flow velocity. No significant correlation was found between fetal heart rate, umbilical artery peak-systolic/end-diastolic ratio, and peak-systolic flow velocity. An upper limit of 3.0 for a normal umbilical artery peak-systolic/end-diastolic ratio was acceptable only if the instantaneous fetal heart rate was greater than or equal to 130 beats/min.     

Reproducibility of fetal ductus venosus blood flow velocity waveforms during first stage of labor

Objectives  

Fetal ductus venosus (DV) blood flow velocity waveforms are significantly altered during contractions in first stage of labor. We have evaluated the reproducibility of these waveforms during and between contractions.     

Postpartum blood flow velocity waveforms of the uterine arteries

Uterine arterial velocity waveforms, recorded by pulsed Doppler technology, demonstrated a significant increase in vascular resistance after the first postpartum day until the fourth to sixth postpartum week. In patients with an isthmic postcesarean hemorrhage, partial placental retention and puerperal endometritis, the corresponding waveforms presented higher diastolic velocity components than was the case for normal puerperal courses, indicating that lower uterine vascular resistance might be associated with these complications.