Early Human Development, 8 (1983) 317-322 Elsevier

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EHD 00517

Nonstress Test in standing and lying women

M. Friedman, M.Y. Divon, E.Z. Zimmer *, I. Goldstein, B.A. Peretz and E. Paldi

Department of Obstetrics and Gynecology “B’: Rambam Medical Center, Technion, Faculty of Medicine, Haifa, Israel

Accepted for publication 30 June 1983

Summary

The effect of the maternal postural position on the Nonstress Test (NST) was evaluated in 14 normal pregnancies at 38-40 weeks of gestation. Each woman was studied for two periods of 30 min, each in the standing and left lateral recumbent positions.

Comparing both positions no significant difference was found in the number of fetal movements and heart rate accelerations. The total surface area of accelerations (TSAA) was significantly larger in the standing position.

maternal postural position; Nonstress Test; total surface area of acceleration

Introduction

The Nonstress Test (NST) has become one of the most important parameters in the evaluation of fetal well being. The advantage of the traditional left lateral recumbent position adopted by most of us when performing the NST has not been scientifically established.

Since women spend a considerable amount of time during the day in the upright position, an investigation was undertaken in order to define the objective difference in fetal activity between the maternal standing and lying position.

Materials and Methods

Informed consent was obtained from 14 healthy pregnant women at 38-40 weeks of gestation. All fetuses were normal and in the vertex presentation. The study was

* To whom all correspondence should be addressed.

037%3782/83/$03.00 0 1983 Elsevier Science Publishers B.V.

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performed at midmorning, 2 h after a standard breakfast. No smoking or medica- tions were allowed. Using an HP-8030A cardiotocograph, abdominal fetal ECG was recorded. Fetal movements perceived by the mother or recognized by the observer were recorded too. All women were tested in both the standing and left lateral recumbent position. The recording lasted 30 min in each position and there was a random assignment to the first and second order. There was no planned equilibra- tion period between the study periods. The NST recording was continued im- mediately after a change in position, allowing only a very short pause for good adjustment of the transducers.

The following parameters were analysed on each strip. (1) Number of fetal movements. (2) Number of fetal heart rate accelerations. (3) Total surface area of accelerations (TSAA). The measurements of TSAA were performed as previously described for decelera- tions [6].

An acceleration was defined as an increase in fetal heart rate of at least 10 beats per min above the baseline, lasting 10 s or more.

The Wilcoxon matched pairs signed-ranks test was used for statistical analysis.

Results

NST recording in the same woman in the erect and lying position is demonstrated in Figs. 1 and 2. Another example is presented in Figs. 3 and 4. Similar patterns were observed in other cases too. Although it seemed that the fetuses were more active while the mothers were standing, no significant differences were observed between the two positions using the usual NST parameters which are number of

Fig. 1. Parturient A: NST in the lying position.

Fig. 2. Parturient A: NST in the standing position

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Fig. 3. Parturient B: NST in the lying position.

Fig. 4. Parturient B: NST in the standing position.

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TABLE I

Total number of fetal heart rate accelerations per 30 min

Lying Standing

5 19 I 10

13 11 11 I 15 13

8 13 12 8 11 14 11 6

9 5 9 12 8 11

11 8 10 7

n.s.

fetal body movements and heart rate acceleration (Table I). It is important to note that all fetal movements were accompanied by accelerations.

Using the units of TSAA a significant difference was found in favor of the standing position (P < 0.01). The area per single acceleration was also significantly larger in the upright position (Table II).

To enable a further randomized comparison within and between the two postural positions, each recording was subdivided into two epochs, 15 min each. There was no significant difference between the TSAA of the two epochs in the same position,

TABLE II

Total surface area per acceleration

Lying Standing

876 624 736 642 603 106

1081 303 525 526 533 642 658 71d

P c: 0.01

1337 809 908

1032 946

1129 1361

906 689

1360 826 154 538 670

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but there was a significant difference (P < 0.01) in favor of each epoch in the standing position compared to each epoch in the lying position.

Discussion

Large maternal hemodynamic changes occur during pregnancy. Evaluating the effect of different maternal postural positions, a decrease was found in cardiac output and placental blood flow in the upright position. In the lying position on the other hand, an increase was noted [3-51. The relationship between maternal posture and perceived fetal movements was investigated and a reduction in movements was reported in the standing parturients [2-71.

To the best of our knowledge there is no other antenatal study with objective measurements of fetal heart activity in different maternal postural positions. In our study which compared the standing and lying positions, we could not find any significant difference in the number of fetal movements and heart rate acceleration. The only difference was in the TSAA. Until now FHR acceleration was usually defined as an increase in FHR which is at least 15 beats/mm more than the baseline value and lasts 15 s or more.

Recently a differentiation to small and large accelerations was suggested. Com- pared to mature fetuses, preterm fetuses were found to have less major acceleration and a smaller acceleration area [l]. In a different study [4] large accelerations were associated with 99.6% of fetal movements, while small accelerations were associated with only 82.4% of fetal movements. Although the definition of small and large accelerations was different in these studies, it was obvious that the type and pattern is of importance. We believe that instead of speaking of “large” and “small” accelerations it would be more accurate to measure the TSAA. Why the TSAA is greater in the standing position is not yet clear. It is possible that these changes represent fetal heart reaction to the changes in maternal hemodynamic state. It could also be speculated that fetal movements are more vigorous in the standing position.

From a clinical point of view it is important to know that fetal monitoring in the lying mother does not represent the true fetal state during daytime. During the day most of the parturients are active and fetal behavioral states in such situations need further investigation.

References

1 Bond, A.P. and Beazley, J.M. (1982): A comparison of non-stressed cardiotocographs in normal preterm and term pregnancy. J. Obstet. Gynecol., 3, 81-84.

2 Minors, D.S. and Waterhouse, J.M. (1979): The effect of maternal posture, meals and time of the day on fetal movements. Br. J. Obstet. Gynecol., 86, 717-723.

3 Pritchard, J.A. and Macdonald, P.C. (1980): Maternal adaptation to pregnancy. In: Obstetrics, 16 edition, pp. 221-259. Editor: Williams. Appleton-Century-Crofts, New York, NY.

4 Rabinowitz, R., Persitz, E. and Sadovsky, E. (1983): The relation between fetal heart rate accelerations and fetal movements. Obstet. Gynecol., 61, 16-18.

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5 Suonio, S., Simpanen, A.L., Olkkonen, H. and Hating, P. (1976): Effect of the left lateral recumbent position compared with the supine and upright positions on placental blood flow in normal late pregnancy. Ann. Clin. Res., 8, 22-26.

6 Tejani, N., Mann, L.I., Bhakthavathsalan, A. and Weiss, R.R. (1975): Correlation of fetal heart rate - uterine contraction patterns with fetal scalp blood pH. Obstet. Gynecol., 46, 392-396.

7 Zimmer, E.Z., Peretz, B.A., Marcovici, R., Goldstein, I., Eyal, A. and Paldi, E. (1982): Correlation of fetal movements with maternal posture. J. Obstet. Gynecol., 3, 85-86.