Comparison of umbilical artery Doppler velocimetry between maternal ...

Ultrasound Obstet Gynecol 1998;11:415–418

Comparison of umbilical artery Doppler velocimetry between maternal supine position and complete left lateral position in predicting obstetric complications E. Ryo, T. Okai, K. Takagi*, S. Okuno*, M. Sadatsuki, M. Kaneko* and Y. Taketani Department of Obstetrics and Gynecology, Faculty of Medicine, University of Tokyo; *Tokyo Koseinenkin Hospital, Tokyo, Japan

Key words:

RESISTANCE INDEX, UMBILICAL ARTERY, MATERNAL POSITION, STRESS TEST, SUPINE POSITION,

COMPLETE LEFT LATERAL POSITION

ABSTRACT The aim of this study was to compare the predictive value of umbilical artery Doppler velocimetry in women in the supine position with that in women in the complete left lateral position as a screening test for abnormal obstetric outcomes. Umbilical artery resistance index (RI) was measured at 27–29 weeks and 35–37 weeks in 202 pregnant women. The measurements were performed with the mother in the supine position in 100 cases (supine group), and in the complete left lateral position in 102 cases (lateral group). Predictive values of the tests for abnormal outcomes (small for gestational age, fetal distress, pregnancyinduced hypertension) were compared between both groups. When abnormal RIs were defined as being greater than the 90th centile in the supine group, the sensitivities for any of the abnormal outcomes at 27–29 weeks were 18% in the supine group and 6% in the lateral group; the positive predictive values were 30% and 25%, respectively. For measurement at 35–37 weeks, the sensitivity and positive predictive value were 29% and 45%, respectively in the supine group, and 0% in both cases in the lateral group. When abnormal RIs were defined as being greater than the 90th centile in the lateral group, the sensitivities at 27–29 weeks were 41% in the supine group and 6% in the lateral group; the positive predictive values were 44% and 8%, respectively. At 35–37 weeks, the sensitivity and positive predictive value were 53% and 43% in the supine group, and 6% and 8% in the lateral group. Umbilical artery Doppler velocimetry when the mother was in the complete left lateral position was of little value as a screening test. However, when the mother is in the

supine position, it may serve as a kind of stress test and disclose latent obstetric abnormalities in certain cases.

INTRODUCTION The effect of maternal posture on umbilical arterial flow has been studied previously. For instance, Katwijk and Wladimiroff1 reported that a change in maternal posture from the standing to the supine position resulted in an increase in the pulsatility index (PI) of the umbilical artery. Furthermore, Marx and colleagues2 demonstrated that umbilical artery systolic/diastolic (S/D) ratios were significantly higher in women in the supine than in the semilateral position. The likely explanation for the elevation of the indices of umbilical blood flow in the supine position is that this position is associated with compression of the inferior vena cava and the lower aorta by the enlarging uterus, thus influencing maternal cardiac output and, as a result, the placental circulation. Recent evidence3 suggests that the results of the non-stress test differ according to whether the mother is in the supine or left lateral position. These findings indicate that Doppler velocimetry is influenced by the mother’s position. However, there has been no investigation of the effect of the maternal position on the accuracy of the examination. With this in mind, we examined the influence of maternal posture, i.e. supine or complete left lateral, on the clinical usefulness of umbilical artery Doppler velocimetry, namely the resistance index (RI), in predicting a poor obstetric outcome.

Correspondence: Dr E. Ryo, Musashino Red Cross Hospital, 1-26-1, Kyonan-Cho, Musashino-City, Tokyo 180, Japan

415

O R I GI N A L PAP E R

AMA: First Proof

Received 16–12–96 Revised 8–9–97 Accepted 17–9–97

Supine position and complete left lateral position

Ryo et al.

METHODS A total of 202 consecutive pregnant Japanese women who received prenatal care at both 27–29 weeks and 35–37 weeks, and who were delivered in our hospital in 1993–94 were recruited into the study. Multiple pregnancies and cases of major fetal malformations were excluded. Informed consent was obtained from each subject. In all cases, the gestational age had been determined by ultrasound dating at an early stage of pregnancy. In 100 cases, Doppler flow analyses were performed with the mother in the supine position after a period of at least 5 min in the position at both 27–29 weeks and 35–37 weeks (supine group). In 102 cases, Doppler flow analyses were performed with the mother in the complete left lateral position in the same way at the same gestational periods (lateral group). Each woman was alternately allocated to one of the two groups. The reason for selecting these periods was that the possible maternal hemodynamic changes due to a supine position seem to appear after 28 weeks and the vena cava is compressed in the majority of pregnant women in the late third trimester. A Toshiba SSA-270A system with a 3.5-MHz transabdominal transducer was used. The high-pass filter was set at 140 Hz and the sample size was 3 mm. Measurements were not made during periods of fetal breathing or excessive activity. At least five stable consecutive waveforms were required before measurements were made. The RI was calculated from waveforms obtained from the umbilical artery. The management during pregnancy and delivery was conducted with the clinicians blinded to the measured RI values. We analyzed the RI values in relation to abnormal obstetric outcomes such as small for gestational age (SGA), pregnancy-induced hypertension and fetal distress. SGA was defined as a birth weight less than the 10th centile of the Japanese birth weight chart4. This standard was adjusted for maternal parity and fetal sex. The diagnosis of pregnancy-induced hypertension was made when the blood pressure was ≥ 140 mmHg for systolic pressure and/or ≥ 90 mmHg for diastolic pressure. The diagnosis of fetal distress was based on the fetal heart rate pattern such as loss of variability, late deceleration, severe variable deceleration and continuous bradycardia. The diagnosis was made by obstetricians who were unaware of the results of the Doppler studies. The RI values were expressed as the median (95% confidence interval). Abnormal RIs were defined as those over the 90th centile for corresponding gestational periods in

each maternal position. We analyzed the outcome of pregnancy in each group in relation to the abnormal RIs obtained from both supine and lateral groups at corresponding gestational periods. Comparison of the RI values and the profiles between the two groups was performed by the Mann–Whitney U test and Student’s t test, respectively. Categorical data were analyzed by means of Fisher’s exact probability method. Statistical significance was considered when p < 0.05.

RESULTS There were no significant differences in the maternal age, birth weight, week of delivery and incidence of SGA, pregnancy-induced hypertension and fetal distress between patients in the supine group and those in the lateral group (Table 1). The RI values were 0.69 (0.682–0.709) (n = 100) for the supine group and 0.67 (0.665–0.689) (n = 102) for the lateral group at 27–29 weeks’ gestation with a significant difference detected (p = 0.0437). The values of the 90th centile were 0.795 for the supine group and 0.760 for the lateral group. At 35–37 weeks, the RI values were 0.63 (0.622–0.652) (n = 100) for the supine group and 0.62 (0.606–0.630) (n = 102) for the lateral group (p = 0.1136), and the values of the 90th centile were 0.740 and 0.700, respectively. Table 2 shows the sensitivity, specificity and predictive values of umbilical artery RI at 27–29 weeks for all women with obstetric complications. When the definition of an abnormal RI was greater than the 90th centile of the supine group, the sensitivities for any abnormal outcomes were

Table 1 The profiles of the supine group and the lateral group. Data are presented as mean ± standard deviation or number

Age (years) Week of delivery Birth weight (g) SGA FD PIH Any of SGA, FD, or PIH

Supine group (n = 100)

Lateral group (n = 102)

Significance

30.6 ± 4.27 39.6 ± 1.14 3095 ± 437.5 7 10 4 17

30.3 ± 3.67 39.5 ± 1.23 3090 ± 414.2 5 12 2 16

p = 0.5143 p = 0.3001 p = 0.9436 p = 0.5662 p = 0.8221 p = 0.4426 p = 0.8506

SGA, small for gestational age; FD, fetal distress; PIH, pregnancyinduced hypertension Comparison of the values between the groups was performed by Student’s t test or Fisher’s exact probability method

Table 2 Sensitivity, positive predictive value (PPV), specificity and negative predictive value (NPV) of umbilical artery resistance index (RI) at 27–29 weeks for any of small for gestational age, fetal distress or pregnancy-induced hypertension Abnormal RI

Group

Sensitivity

PPV

Specificity

NPV

> 90th centile in the supine group

supine

18% (3/17) p = 0.601 6% (1/16)

30% (3/10) p > 0.99 25% (1/4)

92% (76/83) p = 0.2059 97% (83/86)

84% (76/90) p > 0.99 85% (83/98)

41% (7/17) p = 0.0391 6% (1/16)

44% (7/16) p = 0.0882 8% (1/12)

89% (74/83) p = 0.813 87% (75/86)

88% (74/84) p = 0.3959 83% (75/90)

lateral > 90th centile in the lateral group

supine lateral

Comparison of the values between the groups was performed by Fisher’s exact probability method

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Ryo et al.

18% in the supine group and 6% in the lateral group; the positive predictive values were 30% and 25%, respectively. When an abnormal RI was defined as being greater than the 90th centile in the lateral group, the sensitivities for any abnormal outcomes were 41% in the supine group and 6% in the lateral group; the positive predictive values were 44% and 8%, respectively. Table 3 shows the sensitivity, specificity and predictive values for any of the obstetric abnormalities at 35–37 weeks. When an abnormal RI was defined as a value over the 90th centile in the supine group, the sensitivity and positive predictive value were 29% and 45% in the supine group, and both were 0% in the lateral group. The sensitivity and positive predictive value were 53% and 43% in the supine group, and 6% and 8% in the lateral group when an abnormal RI was defined from the lateral group. All sensitivities and positive predictive values of the supine group were higher than those of the lateral group. In particular, the sensitivities in the supine group at both 27–29 and 35–37 weeks were significantly higher than those in the lateral group when abnormal RIs were defined as over the 90th centile in the lateral group (p = 0.0391 and p = 0.0066, respectively). There were no significant differences in specificities and negative predictive values between the two groups.

DISCUSSION The incidence of supine hypotensive syndrome is around 10%. However, radiological and manometric5,6 studies have demonstrated that the inferior vena cava is occluded in the majority of pregnant women who are in the supine position. It is likely that the maternal supine position may perturb the fetal hemodynamic system despite the absence of maternal symptoms. In contrast, the influence on fetal hemodynamics is least when the mother is in the complete left lateral position compared with any other position7. In this study, we compared the clinical usefulness of umbilical artery Doppler velocimetry between women in the supine vs. the complete left lateral position with the aim of determining the influence of compression of the inferior vena cava and lower aorta on Doppler measurement and its clinical relevance. The umbilical artery blood flow velocity waveform index in the mothers in the supine position was higher than

that in the complete left lateral position at 27–29 weeks’ gestation. The elevation of the indices in the supine position may be explained by the influence of the compression of the vena cava or the lower aorta. In other words, the supine position of the mother may be more of a burden to the fetus. The compression of the vena cava or the lower aorta is supposed to reduce the blood flow in the uterus like the contraction of the uterus occurring during the oxytocin challenge test. Hence, the analysis of the umbilical artery blood flow velocity waveform in the supine position can be regarded as a kind of stress test to detect latent obstetric abnormalities. This may well explain the higher sensitivity in the supine group compared with that in the complete left lateral group, especially when the abnormal RIs were defined from the lateral group being without stress due to maternal position. On the other hand, the umbilical artery velocity waveform recorded from the mother in the complete left lateral position was hardly workable as a screening test. It is reasonable to speculate that the lateral position does not influence fetal hemodynamics and hence fails to unravel underlying abnormalities. In any event, it is to be noted that maternal position should be taken into account when evaluating the data of Doppler velocimetry. There have been a number of studies on the association between blood flow velocimetry of the umbilical artery and abnormal obstetric outcome. For instance, an abnormal umbilical artery S/D ratio was reported8 to be a good predictor of growth retardation. Rochelson and coworkers9 reported that the sensitivity of the S/D ratio as a predictor of fetal distress was about 60%. However, Beattie and Dornan10 concluded that umbilical artery velocity waveform analysis was of little value if employed as a screening test for small-for-dates babies. The test was further shown to be of limited value in terms of the prediction of clinical fetal distress in labor11. One of the reasons for the disagreement might be the influence on the fetal circulation induced by the maternal posture, because the degree and duration of the vena cava compression varied among the cases. In conclusion, the umbilical artery velocity waveform when a mother is in the supine position may serve as a stress test to disclose impaired fetal well-being. When umbilical artery velocimetry is conducted with the mother in the complete left lateral position, it is a poor screening test for fetal disorders.

Table 3 Sensitivity, positive predictive value (PPV), specificity and negative predictive value (NPV) of umbilical artery resistance index (RI) at 35–37 weeks for any of small for gestational age, fetal distress or pregnancy-induced hypertension Abnormal RI

Group

Sensitivity

PPV

Specificity

NPV

> 90th centile in the supine group

supine

29% (5/17) p = 0.0445 0% (0/16)

45% (5/11) p > 0.99 0% (0/1)

93% (77/83) p = 0.061 99% (85/86)

87% (77/89) p = 0.6863 84% (85/101)

53% (9/17) p = 0.0066 6% (1/16)

43% (9/21) p = 0.0545 8% (1/12)

86% (71/83) p = 0.8244 87% (75/86)

90% (71/79) p = 0.264 83% (75/90)

lateral > 90th centile in the lateral group

supine lateral

Comparison of the values between the groups was performed by Fisher’s exact probability method

Ultrasound in Obstetrics and Gynecology 417 AMA: First Proof


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Ryo et al. 7. Kinsella SM, Lohmann G. Supine hypotensive syndrome. Obstet Gynecol 1994;83:774–88 8. Fleischer A, Schulman H, Farmakides G, Bracero L, Blattner P, Randolph G. Umbilical artery velocity waveforms and intrauterine growth retardation. Am J Obstet Gynecol 1985;151: 502–5 9. Rochelson B, Schulman H, Farmakides G, Bracero L, Ducey J, Fleischer A, Penny B, Winter D. The significance of absent end-diastolic velocity in umbilical artery waveforms. Am J Obstet Gynecol 1987;156:1213–18 10. Beattie RB, Dornan JC. Antenatal screening for intrauterine growth retardation with umbilical artery Doppler ultrasonography. Br Med J 1989;298:631–5 11. Newnham JP, Patterson LL, James IR, Diepeveen DA, Reid SE. An evaluation of the efficacy of Doppler flow velocity waveform analysis as a screening test in pregnancy. Am J Obstet Gynecol 1990;162:403–10

418 Ultrasound in Obstetrics and Gynecology AMA: First Proof