Doppler ultrasound and fetal activity.

The possibility that Doppler ultrasound, as used in routine fetal monitoring by external cardiotocography, might stimulate fetal activity was investigated. A mean increase in fetal activity of over 90% was found, as judged by the fetal movement count.     

Influence of Doppler ultrasound on fetal activity.

A randomised and double blind study of 100 subjects and 50 controls was performed to confirm or refute a report from Cardiff in 1975 that continuous Doppler ultrasound, as used in fetal heart rate monitoring, increases fetal movement by over 90%. The results showed such an effect to be most unlikely (power greater than 0.99). A total of 150 pregnant mothers recorded fetal movements for 30 minutes while connected to a specially modified cardiotocograph, the ultrasound being switched on at random for either the first or second 15 minutes in 100 of the patients. The mean difference in 15 minute movement count, with and without ultrasound, among the 100 patients was 0.2 of a movement (SD 12.7; p greater than 0.6 by two tailed Wilcoxon matched pairs signed ranks test). The control group showed a mean difference of 2.6 movements (SD 12.1; p greater than 0.2). Results of a pilot study suggested that the observations in the earlier report may have been influenced by mechanisms unrelated to ultrasound.     

Comparison between subjective and ultrasound assessments of fetal movement.

Forty pregnant women participated in a study to compare subjective with ultrasound assessments of fetal movements. A real-time ultrasound scanner was used. Movements were recorded for 45 minutes in all cases. There was a significant positive correlation between the number of movements recorded by the two methods, but the 95% confidence limits were wide and no correlation was found in those patients who recorded fewer than 20 movements in the study period. Thus "false-positive" information may be obtained from purely subjective data, and in patients reporting low "kick counts" fetal activity should be assessed from real-time ultrasound recordings.     

Doppler ultrasound method for detecting human fetal breathing in utero.

An audible Doppler ultrasound method for detecting human fetal breathing movements in utero has been developed. The frequencies synchronous with fetal breathing movements probably originate from the lung rather than the chest wall. This method is much cheaper and simpler than the ultrasound A-scan method and is suitable for screening large numbers of people.     

Doppler ultrasonographic assessment of maternal and fetal blood flow in abnormal canine pregnancy

The aim of this study was to describe the changes of uterine artery, umbilical artery and fetal abdominal aorta, renal and internal carotid arteries blood flow in abnormal canine pregnancy. Twenty-two, Brucella-negative pregnant bitches were retrospectively classified into abnormal (which had either interrupted their pregnancy between days 52 and 60 or had perinatal death >60% of the litter; n=11) and normal (which had delivered healthy puppies at term; n=11). In all the animals, color and pulsed-wave Doppler examinations of uterine artery were conducted every 10 days from Day 20 to 50 from estimated luteinizing hormone peak. Doppler ultrasonography was also conducted in the fetuses to assess umbilical artery, abdominal aorta, renal and internal carotid arteries from Day 40 to 60 of gestation. Throughout the study, resistance index (RI) of uterine, umbilical and fetal renal arteries decreased up to -15% compared to -36% (P<0.01), -11% compared to -23% (P<0.05) and 2% compared to -13% (P<0.05), respectively in the abnormal and normal bitches. Fetal abdominal aorta and internal carotid did not differ between groups (P>0.05). It is concluded that in dogs, uterine artery, umbilical artery and fetal renal artery RI differ between normal and abnormal gestation being useful for the prediction of adverse obstetric outcome.     

Estimation of fetal weight by ultrasound.

Estimation of fetal size by ultrasound has supported two recent concepts of fetal growth. Firstly, the normal weight gain is constant from 28 weeks of gestation until several weeks after term; about 27 g/day. Secondly, the average weight of fetuses born preterm is lower than the average weight of fetuses of the same gestational age who remain in utero. This means that up to 40% of infants born at 28-30 weeks of gestation are small-for-gestational age, when related to the biological optimum. Unfortunately, the test-retest variation of fetal weight estimation is as much as 50% of the standard deviation of the gestational-age-specific fetal weight distribution. This means that fetal growth has to be followed for many weeks to document statistically significant deviations. No study has, as yet, demonstrated the value of this approach to distinguish between intrauterine growth retardation and growth along low centiles by fetuses of reduced growth potential.     

Noninvasive assessment of sympathetic vasoconstriction in human and rodent skeletal muscle using near-infrared spectroscopy and Doppler ultrasound.

The precise role of the sympathetic nervous system in the regulation of skeletal muscle blood flow during exercise has been challenging to define in humans, partly because of the limited techniques available for measuring blood flow in active muscle. Recent studies using near-infrared (NIR) spectroscopy to measure changes in tissue oxygenation have provided an alternative method to evaluate vasomotor responses in exercising muscle, but this approach has not been fully validated. In this study, we tested the hypothesis that sympathetic activation would evoke parallel changes in tissue oxygenation and blood flow in resting and exercising muscle. We simultaneously measured tissue oxygenation with NIR spectroscopy and blood flow with Doppler ultrasound in skeletal muscle of conscious humans (n = 13) and anesthetized rats (n = 9). In resting forearm of humans, reflex activation of sympathetic nerves with the use of lower body negative pressure produced graded decreases in tissue oxygenation and blood flow that were highly correlated (r = 0.80, P < 0.0001). Similarly, in resting hindlimb of rats, electrical stimulation of sympathetic nerves produced graded decreases in tissue oxygenation and blood flow velocity that were highly correlated (r = 0.93, P < 0.0001). During rhythmic muscle contraction, the decreases in tissue oxygenation and blood flow evoked by sympathetic activation were significantly attenuated (P < 0.05 vs. rest) but remained highly correlated in both humans (r = 0.80, P < 0.006) and rats (r = 0.92, P < 0.0001). These data indicate that, during steady-state metabolic conditions, changes in tissue oxygenation can be used to reliably assess sympathetic vasoconstriction in both resting and exercising skeletal muscle.     

Conceptus ecobiometry and triplex Doppler ultrasonography of uterine and umbilical arteries for assessment of fetal viability in dogs

The objectives were to: 1) evaluate blood flow in the uterine (UA) and umbilical (Uma) arteries in the pregnant bitch, by measuring the resistive index (RI) and pulsatility index (PI); 2) to note the presence or absence of the early diastolic notch and diastolic flow in the UA and Uma flow waveforms, respectively; and 3) perform conceptus ecobiometry for fetal growth assessment during pregnancy. Six healthy bitches were examined on approximately Days -44, -42, -36, -31, -28, -25, -21, -18, -14, -8, -4, and -2 of pregnancy (whelping = Day 0). Triplex Doppler and B-mode ultrasonography were used to assess blood flow and conceptus ecobiometry. All pregnancies ended with a normal whelping and birth of live puppies. Prior to whelping, all conceptus dimensions increased significantly, whereas RI and PI of both the Uma and UA decreased significantly. For the UA, RI and PI were (mean ± SEM) 0.95 ± 0.02 and 2.75 ± 0.41, respectively, on Day -44, and were 0.60 ± 0.01 and 0.99 ± 0.03 on Day -4. For the Uma, RI and PI were 0.99 ± 0.01 and 2.42 ± 0.03 on Day -31, and were 0.62 ± 0.01 and 1.15 ± 0.02 on Day -4. The complete disappearance of the early diastolic notch in the UA, and the appearance of diastolic flow in the Uma occurred on Days -16 ± 5 and -21 ± 1. The authors concluded that UA and Uma perfusion were important end points to assess fetal vitality in bitches. Furthermore, the current reference values provided a baseline for monitoring normal and abnormal pregnancies in bitches.     

Maternal perception of fetal motor activity.

A technique using real-time ultrasound for comprehensive recording of fetal motor activity was used in 20 subjects in the third trimester of pregnancy. Maternal awareness of fetal movement correlated with the number of fetal parts contributing to the movement but not with maternal parity or obesity, gestational age, placental site, or duration of the fetal movement. Some subjects recorded fetal breathing, passive fetal displacement, and Braxton Hicks''s contractions as fetal movement. Most of our subjects were consistent and accurate in their perception of major fetal movements, but a few were inconsistent and one was completely unaware of major fetal movements. These results suggest that kick counts kept by most mothers will be accurate. Low counts of fetal movement should be an indication for fetal monitoring by other means and not, unconfirmed, for intervention.     

Calf blood flow and posture: Doppler ultrasound calibrated by plethysmography.

A procedure was developed that enables measurement of rapid variations in calf blood flow during voluntary rhythmic contraction of the calf muscles in supine, sitting, and standing positions. During the exercise, maximum blood velocity is measured by Doppler ultrasound equipment in the popliteal artery. The Doppler signals are calibrated by plethysmography to enable calculation of blood flow during exercise in ml.100 ml-1.min-1. Knowledge of the cross-sectional area of the vessel and the angle of insonation is not required in this procedure. Evaluation of the calibration method with 10 healthy volunteers showed that for each subject a new calibration was necessary after a change in posture; the relationship between the blood flow and the maximum Doppler frequency averaged over one heart cycle was linear for each calibration.     

Early pregnancy assessment with transvaginal ultrasound scanning.

OBJECTIVE: To establish normal parameters in early pregnancy through transvaginal ultrasonography so that gestational age can be determined and to correlate the sonographic findings with serum human chorionic gonadotropin (hCG) levels calibrated against the first international reference preparation standard. SETTING: Infertility clinic. PATIENTS: Thirty-five women with normal intrauterine pregnancy. INTERVENTIONS: Serial measurement of the serum hCG level and the diameter of the gestational sac through transvaginal ultrasonography. MAIN RESULTS: The gestational sac could not be visualized when the hCG level was less than 1100 IU/L. The average growth rate of the sac was 0.9 mm/d. The threshold values for sac diameter, serum hCG level and gestational age below which the yolk sac was not visible were 3.7 mm, 1900 IU/L and 36 days respectively; the corresponding values above which the yolk sac was always visible were 6.7 mm, 5800 IU/L and 40 days. The threshold values below which cardiac activity was not visible were 8.3 mm, 9200 IU/L and 41 days respectively, and the corresponding values above which cardiac activity was always visible were 14.0 mm, 24,000 IU/L and 46 days. The mean gestational ages and the 95% confidence and prediction intervals were tabulated so that measurement of the gestational sac diameter could be used to estimate gestational age early in normal pregnancy. CONCLUSIONS: Transvaginal ultrasonography enables detection of an intrauterine sac and reliable estimation of gestational age on the basis of sac dimensions before an embryo can be seen.     

Combined one- and two-dimensional ultrasound system for monitoring fetal breathing movements.

A combined one- and two-dimensional ultrasonic system for monitoring respiratory movements in the human fetus has been developed. A real-time cross-sectional image of the fetal chest at the level of the fetal heart can be obtained, and a time motion recording of fetal respiratory movements can then be written on a strip-chart recorder. Combining the features of one-dimensional and two-dimensional systems produces an accurate means of investigating fetal breathing movements.     

Fetal activity and fetal wellbeing: an evaluation.

The clinical value of the 12-hour daily fetal movement count (DFMC) as a test of antepartum fetal wellbeing was assessed. The lowest 2-5% of 1654 DFMCs recorded by 61 women who subsequently delivered healthy infants fell below 10 movements per 12 hours. This level was taken as the lower limit of normal for clinical purposes. A normal DFMC in a population at risk was associated with a satisfactory fetal outcome. A low DFMC was associated with a high incidence of fetal asphyxia, and when fetal death occurred fetal movements rapidly diminished and stopped 12 to 48 hours before death. The DFMC is a generally applicable method of monitoring fetal welfare during pregnancy which provides an inexpensive adjunct or even an alternative to the more expensive placental function tests in current use.     

Behavioural assessment of fetal health

The assessment of behavioural activity of the fetus is widely used to assess fetal health in clinical practice as part of the biophysical profile as well as the nonstress test. Considerable information regarding normal activity patterns of healthy human fetuses have been obtained from 24 to 40 weeks gestation. It is this information which has provided the scientific foundation for the development of fetal assessment protocols. Studies in chronically-catheterized fetal sheep have demonstrated that acute hypoxemia leads to an inhibition of fetal breathing movements although prolonged reductions in oxygen delivery to the fetus in the absence of acidemia are associated with adaptation by the fetus and subsequent return to normal incidence of behavioural activity. The behavioural responses of the fetus to specific stimuli including vibroacoustic stimulation have been examined in relation to gestational age as well as type of stimulus, it is proposed that fetal acoustic stimulation could possibly be used to assess fetal neurological function although prior to it being accepted as an universal method for assessing fetal health it is essential that a greater understanding of the mechanisms involved in fetal responses to sound and vibration be determined using appropriate experimental techniques.     

Calf blood flow and posture: Doppler ultrasound measurements during and after exercise.

To investigate the joint effects of body posture and calf muscle pump, the calf blood flow of eight healthy volunteers was measured with pulsed Doppler equipment during and after 3 min of rhythmic exercise on a calf ergometer in the supine, sitting, and standing postures. Muscle contractions seriously impeded calf blood flow. Consequently, blood flow occurred mainly between contractions and reached a plateau that lasted at least the final 100 s of each exercise series. After exercise the blood flow decreased much faster in the sitting and standing postures than in the supine posture. There was no difference in blood flow between various postures during the same submaximal exercise. However, subjects in the standing posture were able to perform exercise with a higher load than in the supine posture, and blood flow in the standing posture could become twice as high as in the supine posture. We conclude that calf blood flow is regulated according to needs; available perfusion pressure determined maximal blood flow and exercise; and compared with the supine posture, the standing posture and calf muscle pump increase the perfusion pressure.     

A morphometric analysis of the fetal craniofacies by ultrasound: fetal cephalometry

We present here a set of 24 standardized linear measurements that describe the growth of different craniofacial structures in the normal fetus from 16 to 36 weeks of gestation. These measurements were taken from 89 pregnant women, who had from 1 to 3 ultrasonographic evaluations during the pregnancy (16, 26, and 36 weeks of gestation). All the values presented here were obtained using the technique described by Escobar et al. The mean and standard deviation was calculated for each measurement and was used to estimate the normal growth pattern of each variable. Approximate confidence intervals for the mean of each variable were constructed for use in identifying unusually low or high values. The confidence intervals are available in graphic form by request. These data will not only contribute to an understanding of fetal craniofacial growth and development in utero, but in addition, it will help to make the diagnoses of mild craniofacial anomalies that would not be detected by the routine ultrasonographic examination. We suggest that this procedure should be included if not in all routine obstetrical ultrasound evaluations, then at least in the more extensive level II obstetrical ultrasound.     

Use of Doppler technology in assessing fetal health

Doppler technology has provided new information about the fetus during intrauterine life. Changes in red cell velocity in the umbilical artery relate well to changes in downstream resistance in the placenta. Resistance (or more correctly impedance) appears to be closely linked to the number of small fetal arterioles in the tertiary stem villus. Placental pathology leading to a reduction in these arterioles is often associated with severe intrauterine growth restriction and poor perinatal outcome. Whilst there is no good evidence that screening women with low risk pregnancies is clinically useful, umbilical artery Doppler information would appear to be useful in the management of pregnancies already identified as at risk. Here abnormal Doppler findings suggest the need for maternal rest, increased fetal surveillance and early delivery when indicated.