Int J Gynecol Obstet.

International

1992, 37: 3-6

Federation

of Gynecology

and Obstetrics

Effect of the vibratory acoustic stimulation patterns of premature fetuses J. Bartnicki”, “Institute

of Perinatal

T. Ratanasirib, Medicine.

Berlin

M. Meyenburga

(Germany)

“Deportment

on fetal heart rate

and E. Saling”

of Obstetrics und Gwecology.

Khon Keen Unieersit~.

Khan Keen

(Thailand)

(Received February 5th. 1991) (Revised and accepted March 24th.

1991)

Abstract The purpose of this study was to examine the heart rate patterns before and after a standardized external vibratory acoustic stimulation in a group of 24 healthy premature fetuses at 32-3.5 weeks gestational age. FHR was analysed on line by Sonicaid Computer System 8000. A significant increase in the number of accelerations and an increase of variation after stimulus were observed. All other FHR patterns such as baseline, high and low episodes did not change significantly.

Keywords: Preterm fetuses; Vibratory acoustic stimulation; Fetal heart rate; Computer analysis of CTG. Introduction

Fetal acoustic stimulation as a tool for the assessment of fetal condition has recently received much attention in the literature. External vibratory acoustic stimulation with an electronic artificial larynx causes changes in FHR [4,6] and movement patterns [3] in term fetuses (3640 weeks gestation) up to 1 h after a 5-s stimulus. However, the effect of this stimulus on premature fetuses has not been so 0020-7292/92/$03.50 0 1992 International Pubished and Printed

well documented. The purpose of this study was to examine the heart rate patterns before and after a standardized external vibratory acoustic stimulus in a group of healthy premature fetuses at 32-35 weeks gestational age. Material and methods

Informed consent was obtained from 24 pregnant women between 32-35 weeks gestational age. Seventeen patients had preterm contractions, 4 incompetent cervix, 3 urinary tract infection (without a rise of body temperature). All women had normal term deliveries that confirmed gestational age and the good health of the fetuses studied. The average gestational age at delivery was 39.1 weeks. No Apgar score was less than 7 at 1 min, and umbilical arterial pH was greater then 7.20 in all cases. All infants were greater than 10th centile and less than 90th of weight for gestational age. All studies were made between 0900 h and 1200 h and were conducted in a quiet room with the patients in a lateral position. Women were studied continuously for 2 h. At the end of the first hour of observation, a 5-s vibratory acoustic stimulus was applied on the surface of the maternal abdomen over the fetal head. The external vibratory acoustic stimulus used in this study was Article

Federation in Ireland

of Gynecology

and Obstetrics

4

Bartnicki

et al.

slight rise of FHR is observed after stimulus to a value of 144.1 f 6.9 beats/min but the change was not statistically significant.

generated with an electronic artificial larynx (Servox Medizin Technik, Germany). FHR was recorded before and after stimulation with a Sonicaid FM 7 external monitor (Oxford Instruments Germany) and was analysed on line by Sonicaid System 8000 (Oxford Sonicaid Limited). The software program and its analysis algorithms originate from work carried out by Dawes and Redman, Oxford, UK [2,12]. An acceleration was defined as being an increase in heart rate > 10 beats/min and lasting > 15 s. Variation was assessed in beats/min and in milliseconds. Variation in milliseconds was calculated as the difference between maximum and minimum pulse intervals for each minute. High and low episodes were assessed in minutes of high and low variation. The thresholds were 32 ms for high variation and 30 ms for low. If the computer fails to find an episode of high variation the thresholds were reduced to 24 ms and 22 ms respectively. Statistical significance between CTG patterns before and after stimulus was determined using a Wilcoxon matched-pairs signed-rank test.

Accelerations

The mean number of accelerations increased significantly (Table 1) after vibratory acoustic stimulation. The increase in the number of accelerations in 45.8% cases was connected with an increase of variation of heart rate. Only in 16.6% cases (n = 4) was there no simultaneous increase of variation. Variation

Table 1 shows statistically significant changes in variation assessed in beats/min after vibratory stimulation. Similarly, there was a significant increase in the variation assessed in milliseconds. In four cases (16.6%) there was an increase of variation without simultaneous increase in the number of accelerations. High episodes

Results

There was an increase in the duration of episodes identified as high episodes from the value 33.2 f 7.8 mm/60 min before stimulation to the value 38.6 f 6.3 mm/60 min. The changes were not statistically significant.

FHR

Low episodes

The mean basal FHR was 139.3 f 9.4 beats/min during the hour before stimulus. A

The low episodes occurred only in live cases before stimulation. In four cases the

Table 1.

Fetal heart rate patterns

before and after vibratory

Accelerations R

(n/60 min) SD

acoustic

stimulation.

Variation

(beats/min)

Variation

(ms)

x

SD

.Y

SD

Before stimulus

15.3

3.0

16.8

5.0

45.1

11.0

After stimulus

23.6

6.2

21.6

4.5

54.2

12.4

P

Increase in %

Int J Gynecol Obstet 37

< 0.05

54.5

< 0.005

28.0

< 0.05

20.3

FHR patterns

episodes disappeared after vibratory stimulation, in one case the duration of low episodes remained unchanged. Discussion

The response to acoustic stimulation has been demonstrated as early as 24 weeks gestation when studied serially from 12 to 32 weeks [l]. Increase of baseline in preterm fetus after vibratory acoustic stimulation has been reported. Gagnon et al. [7] observed statistically significant increase of basal FHR during the first lo-min interval after stimulus in fetuses between 30-32 weeks gestational age. Thomas et al. [13] reported that 79.2% of the preterm fetuses (