Bunn, A E

Odendaal, H J

Theron, A M

Theron, G B

South African Medical Journal (SAMJ)

62January 2005, Vol. 95, No. 1  SAMJORIGINAL ARTICLESUmbilical artery Doppler flow velocimetry is essential in theclinical management of pregnancies where intra-uterine growthrestriction (IUGR) is suspected.1,2 It reduces the number ofperinatal deaths and avoids unnecessary obstetricinterventions.  There is also a significant association betweenan increased resistance index (RI) and complications ofplacental insufficiency.3The implementation of appropriate technologies with provenvalue and accuracy must be considered for use in developingcountries.  The proportion of women with pregnancycomplications in these countries manifests in the profounddifference in maternal mortality ratios and perinatal death rateswhen compared with developed countries.4-7 Umbilical arteryDoppler flow velocimetry has the potential to be of great valuein the clinical management of pregnancies where IUGR issuspected.  However, the more affordable continuous-waveDoppler wavefrom analysers developed initially were quicklyreplaced by pulsed-wave analysers that are incorporated intoexpensive ultrasound scanners.  The benefit of non-invasive,safe and easy-to-use systems soon became too expensive formost health services in developing countries.The Medical  Research Council (MRC) Unit for PerinatalMortality, the MRC and Centre for Scientific and IndustrialResearch (CSIR) worked together to develop a novel andaffordable continuous-wave Doppler analyser (Umbiflow) foruse with a standard personal computer (PC).  The requiredsoftware was developed and the Doppler probe housing theelectronics was powered and connected via the USB port of thePC.  The software is user-friendly and allows input of patient,fetal and neonatal data.  The flow velocity waveforms arerecorded on the computer screen.  The RI, calculated from thewaveform, is then plotted on an appropriate percentile graphagainst the estimated gestational age.This study was conducted to determine the accuracy of theflow velocity waveforms of the umbilical artery as measuredusing the Umbiflow both with regard to systematic andrandom variations when compared with a commercialstandard (Sonicaid Vasoflow 4, Oxford Instruments).  The RIwas used for all comparisons.  Care was taken to include thegestational age range (24 - 40 weeks) and sufficient numbers ofpatients with abnormal values (≥ 95th percentile).Patients and methodsA cohort study was conducted.  Consecutive patients referredComparison between a newly developed PC-based Dopplerumbilical artery waveform analyser and a commercial unitG B Theron, A M Theron, H J Odendaal, A E BunnObjectives. To determine the accuracy of the resistance index(RI) of flow velocity waveforms of the umbilical arterymeasured using a newly developed PC-based continuouswave Doppler device (Umbiflow) with regard to systematicand random variations when compared with a commercialstandard (Vasoflow).Design. A cohort study.Setting. The fetal evaluation clinic (FEC) at TygerbergHospital.Subjects. Patients referred to the FEC at Tygerberg Hospitalwith suspected chronic placental insufficiency.Outcome measures. The correlation coefficients indicating thestrength of the relationship between the two devices and theiragreement using the method of Bland and Altman.Results. A total of 248 patients were studied.  The mean RIs ofthe first Doppler assessment were 0.69 (standard deviation(SD) 0.11) and 0.67 (SD 0.11) using the Vasoflow andUmbiflow respectively.  The Pearson’s correlation coefficientcomparing the RI of the first test was 0.85.  The degree ofagreement between the two methods was excellent, the meandifferences being very small (< 0.024) with tight confidenceintervals. One hundred and ninety-four patients (78.2%) ofpatients remained in the same percentile category with boththe Vasoflow and Umbiflow.Conclusions. The accuracy of the Umbiflow has been proved.A non-significant trend towards slightly lower values needsto be considered.  This could be addressed by changing thepercentile cut-off to slightly lower values.S Afr Med J 2005; 95: 62-64.Department of Obstetrics and Gynaecology, Stellenbosch University, Tygerberg, W CapeG B Theron, MMed (O&G), FCOG (SA), BSc Hons, MDA M Theron, RNH J Odendaal, MMed (O&G), FCOG (SA), FRCOG, MDTechnology Development and Transfer, Medical Research Council, Tygerberg, W CapeA E Bunn, PhDCorresponding author: G B Theron (Department of Obstetrics and Gynaecology,Stellenbosch University, PO Box 19063, Tygerberg, 7505)ORIGINAL ARTICLESto the fetal evaluation clinic (FEC) at Tygerberg Hospital withsuspected placental insufficiency were included in the study.Using Vasoflow and the Umbiflow alternately on each patient,a single observer (AMT) determined the RI using the best valueas determined by auscultation followed by visualisation on ascreen.  Care was taken to do the measurement when the fetuswas not moving, as reflected by constant velocity in theumbilical vein.  Outcomes of the pregnancies were determined.Patients with an RI < 75th percentile (category 1) wereregarded as being at low risk for complications of placentalinsufficiency, and were not given fetal surveillance tests unlessthe clinical condition changed.  Those with an RI ≥ 75 and <95th percentile (category 2) required a repeat Doppler within14 days, and those with RI ≥ 95th percentile (category 3)received more intensive fetal monitoring.  When absent flow(category 4) was detected, patients were admitted to hospitalfor intensive fetal monitoring or delivery.The strength of the relationship between the Vasoflow andthe Umbiflow was determined by calculating correlationcoefficients and the degree of agreement using the method ofBland and Altman.8 A regression analysis was done on thescatter gram depicting the mean RI values on the x-axis and thedifferences on the y-axis to assess differences in the variancesof smaller compared with larger mean values.9 An assessmentof the agreement or differences in category assignments (firstassessment only), according to the percentile index, was madeby calculating a Kappa index.ResultsA total of 248 patients were included in the study.  Gestationalage was confirmed by early ultrasound in 195 patients (78.6%).The most common reasons for referring patients for Dopplerwere poor symphysis-fundus (SF) growth (34.1%), previouspregnancy complications (24.5%), hypertension (19.7%) andpre-eclampsia (14.9%).  The median gestational age at referralwas 30 weeks, with a range of 21 - 40 weeks.The mean RIs of the first Doppler assessment were 0.69(standard deviation (SD) 0.11) and 0.67 (SD 0.11) using theVasoflow and Umbiflow respectively.  A second test was doneon 59 patients (23.8%), and a third test on 13 patients laterduring the pregnancy because their initial and subsequent RIswere ≥ 75th percentile.  In this second assessment the mean RIswere 0.69 (SD 0.10) and 0.66 (SD 0.10) and the RIs for the thirdtest were 0.76 (SD 0.12) and 0.75 (SD 0.11) using the Vasoflowand Umbiflow respectively.  The correlation coefficientscomparing the RI as measured using the Vasoflow andUmbiflow (Table I) and the degree of agreement between thetwo methods, calculated according to the method of Bland andAltman,8 are shown in Table II.  Fig. 1 is a scattergram of themean values of the first assessment using the two instruments(x-axis) and the differences between the two instruments (y-axis).  The middle horizontal line is the mean difference andthe other two horizontal lines 2 SDs above and below the meandifference.  The correlation coefficient of a regression analysisassessing the possibility of a difference in the variances of thesmaller compared with the larger mean values of the firstassessment results on the scattergram is 0.12 (Fig. 1).  Thenumber of patients remaining in the same percentile categoryand those who shifted to another category are shown in Table III.63January 2005, Vol. 95, No. 1  SAMJTable I. The correlation coefficients of the RI as measured withthe Vasoflow and the Umbiflow1st test 2nd test 3rd testPearson 0.847 0.826 0.957Spearman 0.789 0.731 0.7970.30.20.10.0–0.1–0.20.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1Mean RIVasoflow minus UmbiflowFig. 1. A scattergram of the mean values of the first assessment usingthe two instruments, and the difference between the two instruments.Table II. The mean differences and the distribution of thesedifferences between the Vasoflow and the Umbiflow1st test 2nd test 3rd testN 249 59 13Mean 0.023 0.020 –0.005SD 0.062 0.058 0.037+2SD 0.147 0.136 0.066–2SD –0.100 –0.096 –0.077Table III. Shifts in categories that occurred with the firstassessment between the two instruments according to resistancecategory (N = 248)Umbiflow1 2 3 41 131 14 0 0Vasoflow 2 36 42 1 03 0 3 11 04 0 0 0 1064January 2005, Vol. 95, No. 1  SAMJORIGINAL ARTICLESAntenatal admission was necessary for 110 patients (44.3%)and complications occurred in 152 cases (61.3%).  The mediangestational age at delivery of patients with viable fetuses was38 (27 - 46) weeks.  Spontaneous onset of labour occurred in129 patients (52.0%), induction of labour in 89 (35.9%), electivecaesarean sections in 29 (11.7%) and 2 terminations ofpregnancy were required.  The overall caesarean section ratewas 26.1%.The mean birth weight of viable babies was 2 712 g(665 - 4 294 g), with 30.1% light for gestational age.  There were5 intra-uterine and 5 neonatal deaths (perinatal mortality rate40.3/1 000).DiscussionThe study population met the stated objectives, i.e. it includedpatients across a wide range of gestational age, at high risk forplacental insufficiency, pregnancy complications and poorperinatal outcome.  A significant number of patients hadabnormal RI values.  A valid comparison between the Vasoflowand Umbiflow was therefore possible.The mean RIs of the Vasoflow and Umbiflow differed by ≤ 0.03.  A good correlation between the two instruments wasdemonstrated (Table II).  The more important degree ofagreement was excellent, with the mean differences being verysmall (< 0.024) with tight confidence intervals (Table II).Variability according to size of the smaller compared withlarger mean values on the x-axis of the scattergram was verysmall (Fig. 1). The correlation coefficient of these values (0.12)deviates only very slightly from the horizontal linerepresenting the mean difference on the scattergram.  Thecorrelation coefficient comparing the first measurements of theVasoflow and Umbiflow of 0.8 (Table I) also confirms a smallmean difference through the range of small and larger RIvalues.9 The Kappa index of 0.7 indicates good reproducibility.However, very small differences may cause a shift on thepercentile chart (Table III) that may exclude a patient fromfurther fetal surveillance (i.e. to < 75th percentile).  This wouldaffect the 36 patients who fell into the < 75th percentilecategory with the Umbiflow but in the ≥ 75th but < 95percentile category with the Vasoflow.  If managed according tothe Umbiflow measurements and our protocol they wouldhave been excluded from further surveillance unless theirclinical condition changed, e.g. development of pre-eclampsiain a patient who had only had poor SF growth.  Theappropriateness of the 75th percentile in our protocol needsfurther investigation and possible adjustment to a lowerpercentile.  In addition 3 patients moved from the ≥ 95thpercentile to the ≥ 75th but < 95th percentile.  Our protocolrequires non-stress tests twice weekly in the ≥ 95th percentilecategory whereas in the ≥ 75th but < 95th percentile categorythe Doppler is only repeated 2 weeks later with no additionalsurveillance.  Patients moving up to a higher category wouldundergo unnecessary investigations; however this would beerring on the safe side of caution.The accuracy of the Umbiflow has been proved.  A non-significant trend towards slightly lower values needs to beconsidered.  In our protocol this could be addressed by usingthe 70th percentile rather than the present 75th percentile as thethreshold below which further investigations are notperformed.  The next step will be to conduct field trials toestablish the value of the Umbiflow under field conditions atprimary and secondary levels where more sophisticatedDoppler equipment is unavailable.The authors acknowledge the contribution of Mr J Wallis andcolleagues at the CSIR for their contribution in developing thetechnology of the  Umbiflow system.References1. Westergaard HB, Langhoff-Roos J, Lingman G, Marsal K, Kreiner S.  A critical appraisal ofthe use of umbilical artery Doppler ultrasound in high-risk pregnancies:  use of meta-analyses in evidence-based obstetrics.  Ultrasound Obstet Gynecol 2001; 17: 466-476.2. Neilson JP, Alfirevic Z.  Doppler ultrasound for fetal assessment in high risk pregnancies(Cochrane Review).  In:  The Cochrane Library, 1, 2002.  Oxford:  Update Software.3. Theron GB, Theron AM, Odendaal HJ.  Symphysis-fundus growth measurement followed byumbilical artery Doppler velocimetry to screen for placental insufficiency. Int J GynaecolObstet 2002; 79: 263-264.4. Department of Health.  Why mothers die 1997 - 1999:  The Confidential Enquiries into MaternalDeaths in the United Kingdom. London: HMSO, 2001.5. Saving Mothers 1999 - 2001.  Second Report on Confidential Enquiries into  Maternal Deaths inSouth Africa.  Pretoria: Government Printer, 2003.6. Confidential Enquiry into Stillbirths and Deaths in Infancy:  8th Annual Report.  Maternal and ChildHealth Consortium. London, 2001.7. Saving Babies 2002.  Third Perinatal Care Survey of South Africa.  The MRC Unit for Maternal andInfant Health Care Strategies. Pretoria:  Government Printer, 2003.8. Bland JM, Altman DG.  Statistical methods for assessing agreement between two methods ofclinical measurement.  Lancet 1986; i: 307-310.9. Bland JM, Altman DG.  Comparing methods of measurement:  why plotting differenceagainst standard method is misleading.  Lancet 1995; 346: 1085-1087.Accepted 20 September 2004.

Comparison between a newly developed PC-based Doppler umbilical artery waveform analyser and a commercial unit

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Comparison between a newly developed PC-based Doppler umbilical artery waveform analyser and a commercial unit

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