Influence of meperidine on fetal movements and heart rate beat-to-beat variability in the active phase of labor

Eleven parturients were studied in the active phase of labor. Fetal movements, fetal heart rate, and short-term beat-to-beat variability as well as uterine contractions were evaluated for two 40-minute recording periods before and after maternal intravenous administration of 50 mg meperidine. Meperidine depressed fetal activity and increased the duration and frequency of uterine contractions. Fetal movements were significantly reduced from 156 to 60 and their relative duration from 8.6 +/- 6.0% to 2.4 +/- 2.6% (p less than 0.01). The short-term fetal heart rate beat-to-beat variability was reduced at the baseline period 5.22 +/- 1.02 versus 4.62 +/- 1.47 (p less than 0.05) but not during uterine contractions or fetal movements. The frequency of uterine contractions increased from 3.1 +/- 0.8 to 3.7 +/- 0.7 per 10 minutes (p less than 0.01), and their relative duration from 35.3 +/- 6.9% to 40.1 +/- 5.9% (p less than 0.05).     

Significance of exaggerated fetal heart rate accelerations during active labor

One hundred fifty-three of 1,289 patients (11.9%) monitored during labor were identified as having exaggerated fetal heart rate accelerations (EFHRAs), defined as accelerations of the fetal heart rate above the baseline of 30 beats/min or greater and lasting at least 30 seconds. Comparisons of patients with and without EFHRAs showed that the only difference between the two groups was a higher percentage of nulliparous patients in the EFHRA group. Comparisons of intrapartum complications showed a decreased incidence of meconium staining and an increased percentage of abnormal labor patterns in the EFHRA group. Comparisons of neonatal outcome statistics showed lower perinatal morbidity and higher mean birth weight in the EFHRA group.     

The relationship between uterine contractions, fetal movements and fetal heart rate patterns in the active phase of labor

The relationship between fetal movements, fetal heart rate and uterine contractions was studied with a computerized system in 18 parturients during the active phase of labor. 80% of FHR accelerations and 39% of uterine contractions were associated with fetal trunk movements. The probability of association was greater in longer movements and larger accelerations. 98% of fetal movements which lasted 10-15 s, 98% of accelerations with an amplitude of 25-30 bpm and 96.4% of accelerations with a duration of 40-50 s were associated with fetal trunk movements.     

The fetal sound environment during vibroacoustic stimulation in labor: effect on fetal heart rate response.

Nine pregnant women near term, with medical indications for internal monitoring during labor, were studied to determine the transmission of sound across maternal soft tissues during vibroacoustic stimulation with an electronic artificial larynx. A miniaturized hydrophone was placed transcervically at the level of the fetal neck under ultrasound guidance. Intrauterine sound pressure levels were measured before and during stimulation applied at 1 and 0 cm from the surface of the maternal abdomen. When the electronic artificial larynx was placed at a distance of 1 cm from the maternal abdomen, the intrauterine sound pressure level averaged 75 dB at frequencies between 0-5000 Hz. However, when the electronic artificial larynx was firmly applied on the maternal abdomen, intrauterine sound pressure levels were enhanced by more than 20 dB (P less than .001) and averaged 95 dB at all frequencies between 87-20,000 Hz. Baseline intrauterine sound pressure levels consisted of low-frequency sound with intensity of 85 dB at 12.5 Hz, decreasing to 60 dB at 100 Hz and less than 40 dB above 200 Hz. There was a significant correlation (r = 0.78, P less than .02) between the duration of the first fetal heart rate (FHR) acceleration following stimulus and the overall intrauterine sound pressure level at the time of the stimulus. Our data suggest that a threshold of 94 dB intrauterine sound pressure level is necessary to produce a consistent FHR response during active labor.     

Abnormal fetal heart rate patterns during the active phase of labor: the value of fetal oxygen saturation

Objective: To determine the predictive value of intrapartum fetal oxygen saturation (SO₂) for prediction of an umbilical artery pH less than 7.15 at birth in labors complicated by abnormal fetal heart rate traces. Study design: Eighty-five primigravidas in spontaneous labor complicated by abnormal fetal heart rate traces underwent fetal SO₂ monitoring using the fetal pulse oximetry technique. Cases with an SO₂ of < 30% were delivered by Cesarean section. Umbilical artery pH was measured at birth in all women. Results: With the value set of 30% as the cut-off point of fetal oxygen saturation, the positive predictive value for umbilical artery pH of < 7.15 was 61.5% and the negative predictive value was 95.8%, with a sensitivity of 72% and a specificity of 93%. Conclusions: Fetal pulse oximetry is a promising technique for assessment of fetal well-being during labor and may decrease the number of unnecessary Cesarean sections.     

Determinants of fetal heart rate response to vibroacoustic stimulation in labor

To determine whether the fetal heart accelerates in response to a sound stimulus in labor, 40 women at various stages of labor were chosen at random to receive either a vibroacoustic stimulus or sham stimulus over the fetal head. Subsequent fetal heart rate (FHR) accelerations occurred to a significantly greater extent in study patients. One hundred thirty-two high- and low-risk patients were studied to determine correlations between the acceleration response and other maternal and fetal variables. There was a statistically significant negative correlation between the heart rate response to stimulation and three maternal variables: the degree of cervical dilation, the presence of ruptured membranes, and use of epidural anesthesia. The degree of fetal response did not correlate significantly with fetal distress at delivery or abnormal FHR tracings at the time of stimulation. Fewer than one-fifth of the fetuses manifested variable heart rate decelerations after the stimulation. In light of possible risks, the clinical use of the fetal acoustic stimulation test in labor should wait until its diagnostic value is better defined.     

Fetal subcutaneous scalp PO2 and abnormal heart rate during labor

Intrapartum fetal heart rate and subcutaneous scalp PO2 were continuously measured with a combined electrocardiogram-PO2 needle electrode in 34 patients. The incidence of fetal heart rate abnormalities increased significantly with decreasing subcutaneous PO2, from 0.8% of the 10-minute periods in which subcutaneous PO2 was greater than or equal to 25 mm Hg to 53% of the periods in which subcutaneous PO2 was less than 10 mm Hg.     

Response of fetal heart rate to scalp stimulation related to fetal acid-base status.

The correlation of the response of the fetal heart rate (FHR) to scalp stimulation and the acid-base status of the fetal scalp blood (FSB pH) was studied in 104 term fetuses during labor. The mean FHR was determined for the 5-minute period before the preparation for fetal scalp blood pH determination and 1 minute following FSB pH. The analysis was performed for three pH groups: (a) Normal (pH more than 7.25, = 73); (2) preacidotic (pH 7.20 to 7.25, = 16); and (3) acidotic (pH less than 7.20, = 15). The pH was confirmed at delivery by determination of umbilical cord blood acid-base status. Regression analysis of the number of fetuses responding by changing their heart rate against time was significant only for the nonacidotic fetuses. There was no significant difference in the number of subjects whose mean FHR increased, decreased, or remained unchanged between the three pH groups. Furthermore, there was no difference between the three pH groups in the number of fetuses who demonstrated significant mean heart rate changes (p less than 0.05) following the stimulation compared to those who did not. Further analysis between fetuses in the three pH groups who increased FHR 15 beats/min or more following stimulation did not discriminate between groups. We conclude that scalp stimulation results in a FHR response in all three pH categories. However, the net change in the mean heart rate following the stimulation may be negative or positive. The magnitude and the direction of this change in FHR is not significantly related to FSB pH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alterations of pathological fetal heart rate patterns in labor following vibroacoustic stimulation

Vibroacoustic stimulation of the fetus in labor was previously shown to result in a transient fetal heart rate (FHR) tachycardia followed by a return to prestimulation FHR pattern. We presently report 3 cases in which FHR patterns of repeat decelerations were changed to normal following vibroacoustic stimulation. These changes may be related to the strong fetal movements evoked by the stimulation and removal thereby of a mechanical problem such as cord compression.     

Vibration and acoustic stimulation during labor with external monitoring. Pathology of fetal heart rate]

Vibratory acoustic stimulation was done in patients with an abnormal fetal heart rate tracing in external continuous electronic monitoring during labor, correlating with Apgar score, meconium staining and umbilical cord pH, describing a 83.3% sensitivity, 81.3% specificity and 62.5% positive predictive value. The authors recommend the use of vibratory acoustic stimulation in those cases with an abnormal fetal heart rate tracing in external continuous electronic monitoring, when we can not install internal electronic monitoring or obtain a fetal blood pH on assessment of fetal well-being.     

Heat flux from the fetal scalp during labor and fetal outcome

In 40 deliveries a new variable, heat flux from the fetal scalp, was recorded and correlated with fetal outcome. The heat flux from the fetus, which reflects the temperature gradient between the warmer fetus and the mother was measured by a transducer attached to the fetal scalp after rupture of the membranes. In the last 20 min before delivery we found a statistically significant correlation (p less than 0.05) between heat flux from the fetus and pH of umbilical artery blood. Heat flux in the group with higher pH differed significantly from those with lower pH. We conclude that heat flux measurements could be developed and used for fetal monitoring.     

The extent of fetal heart rate accelerations associated with fetal body movements in relation to the duration of fetal body movement

The temporal relations between fetal body movements and associated fetal heart rate accelerations were shown as the ratios of duration of acceleration or acceleration amplitude and the duration of associated fetal body movements in 44 normotrophic and 40 hypotrophic fetuses (body weights within the 6th to 10th percentiles, n = 19, and less than or equal to the 5th percentile, n = 21) between the 36th and 40th gestational weeks. Related to the duration of associated fetal body movements, hypotrophic fetuses proved to have gradually smaller heart rate accelerations than normotrophic fetuses. Moreover, the acceleration parameters duration and amplitude were dependent on the relative duration of fetal body movements. Short fetal body movements were accompanied by fetal heart rate accelerations of relatively highest degree and vice versa. As a consequence, no comparison is possible between temporally different fetal body movements and their associated heart rate accelerations. Of the two acceleration parameters duration and amplitude, the inclusion of the accelerations amplitude in the above mentioned ratio yielded the most obvious results. Taking into consideration that fetuses with intrauterine growth retardation are often in a state of chronic hypoxia, the ratios of acceleration amplitude and durations of associated fetal body movements indicated different degrees of this metabolic situation.     

Fetal heart rate response to vibratory acoustic stimulation predicts fetal pH in labor

Vibratory acoustic stimulation was performed during labor in 188 instances 60 seconds before fetal scalp puncture was done to determine fetal scalp blood pH. The fetal heart rate response was recorded for both vibratory acoustic stimulation and fetal scalp puncture. No instance of fetal acidosis occurred in the presence of an acceleration to either vibratory acoustic stimulation or fetal scalp puncture. Vibratory acoustic stimulation was more likely to elicit an acceleration than fetal scalp puncture in the nonacidotic fetus. Vibratory acoustic stimulation is less invasive and may be used in some instances in which fetal scalp blood puncture for pH determination is technically impossible.     

Vibro-acoustic stimulation in high-risk pregnancies; maternal perception of fetal movements, fetal heart rate and fetal outcome.

Maternal perception of fetal movement in response to vibro-acoustic stimulation was compared with antenatal fetal heart rate monitoring as a test of fetal well-being in a population of gravidae with high-risk pregnancies (n = 517), admitted to the high-risk ward at Danderyd Hospital, Karolinska Institutet; a total of 2,015 tests were performed. The sensitivity and the specificity of the test compared to the fetal heart rate tracing was 81% and 89% respectively. If the test was performed within 24 hours of delivery, its predictive value for fetal asphyxia (i.e. a 5-minute Apgar score < 7) was 14% (7/49). Ten per cent of the patients felt no fetal movement in response to stimulation (irrespective of gestational age). In five cases where fetal heart rate tracings were pathological, stimulation nonetheless produced fetal movement and fetal outcome was good. Pathological heart rate tracings and no fetal movement in response to stimulation were present in 30 cases (out of 251 with no fetal movements at stimulation), in seven of which the infants had 5-minute Apgar scores < 7. Although many patients underwent repeated vibro-acoustic stimulation, there was no evidence of fetal habituation to the test. On 24 occasions (i.e. 1.2%), the patient denied vibro-acoustic stimulation, mostly because of previous discomfort due to vigorous fetal response. Where resources are limited, maternal perception of fetal movements in response to vibro-acoustic stimulation might be a useful alternative for preliminary screening of high-risk pregnancies.     

Acute effects of maternal cigarette smoking on fetal heart rate and fetal body movements felt by the mother.

Acute effects of maternal cigarette smoking on fetal heart rate (FHR) and fetal body movements felt by the mother (FM) were studied in 51 pregnant volunteers. Thirty four were chronic smokers (6 or more cigarettes per day, with an average of 14 cigarettes/day) and 17 were sporadic smokers (1 to 5 cigarettes per day, with an averaged of 3 cigarettes/day). In both groups the number of FM, fetal reactivity and short-term FHR variability decreased significantly in the 20 minutes following cigarette smoking; a sustained FHR rise of 10 or more beats/min was also found after the cigarette in more than 50% of the cases in the 2 groups. No statistically significant differences were found among the 2 groups when the post-cigarette data were compared. We conclude that maternal cigarette smoking produces important acute effects upon FM and FHR regardless the average daily number of cigarettes smoked by the mother.