TEMPLATE DESIGN © Umbilical artery Pulsatility Index and different reference ranges: Does it really matter? Lo W., Mustafa A., Jahangir F., Ali O., Ramanathan G. Fetal Medicine Unit, Corniche Hospital, Abu Dhabi, UAE Objectives Umbilical artery (UA) Doppler pulsatility index (PI) is one of the most used Doppler parameters to distinguishing between a constitutionally small fetus from one that is growth restricted due to placental insufficiency. Many published reference ranges for UA PI are available. The aim of this study is to compare different values of an increased UA PI  95 th percentile from various references and to review its potential impact on obstetric management. Methods A search for publications of UA PI reference ranges was made. All 95 th percentile UA PI values by gestation from the selected references were obtained and plotted against one another. Five commonly used UA PI reference ranges were reviewed: Parro Cordero et al (1), Harrington et al (2), Arduini et al ( 3), Acharya et al (4) and Merz et al (5). The table below shows the five UA PI charts selected for analysis and their characteristics. Results At 28 weeks gestation, Parra Cordero et al demonstrates a difference of +0.1 and to Harrington and Arduini; and a -0.1 difference to the others. At 32 weeks gestation the PI value of Parra Cordero et al is comparable with Acharya and Merz, however there is at least a difference in Harrington and Arduini et al. When a pregnancy reaches 37 weeks gestation, the PI values between Parra Cordero, Acharya and Merz et al are remarkably similar (1.10, 1.14 and 1.16) while the PI in the others are much higher as This pattern continues at full term when Parra Cordero, Acharya and Merz et al reported a PI of 1.00, 1.09 and 1.09 while Harrington and Arduini et al reported Conclusions References We highlight an important variation in the UA PI values  95 th percentile between different references published. These differences are potentially significant when applied to clinical practice, as an UA PI that has a lower 95 th percentile value could mean more fetal surveillance, more steroid therapy and possible consideration of preterm delivery. Similarly at 37 weeks gestation, a lower 95 th percentile value may lead to increased induction of labour. There is currently no evidence in choosing a particularly reference range over the other. A study comparing the clinical management, pregnancy and neonatal outcomes using different UA PI reference ranges is in progress and will hopefully better answer this question. M. Parra-Cordero, C. Lees, H. Missfelder-Lobos, et al. Fetal arterial and venous Doppler pulsatility index and time averaged velocity ranges. Prenatal diagnosis 2007; 27: 1251–1257 Harrington K, Carpenter RG, Ngyyen M and Campbell S. Changes observed in Doppler studies of the fetal circulation in pregnancies complicated by pre-eclampsia or the delivery of a small for gestational age baby: Cross-sectional analysis. Ultrasound Obstet Gynecol 1995;6:19 Arduini D, Rizzo G. Normal values of Pulsatility Index from fetal vessels: a cross-sectional study on 1556 healthy fetuses. J Perinat Med 1990;18: Acharya G., Wilsgaard T, Berntsen GK, et al. Reference ranges for serial measurements of umbilical artery Doppler indices in the second half of pregnancy. American Journal of Obstetrics and Gynecology 2005, 192: Merz E (ed): Ultrasonography in Obstetrics and Gynaecology, Stuttgart, NY. Authors Parra Cordero et al Harrington et al Published journal Prenat DiagnosisUltrasound of ObGyn Year of publication Study number Cohort population All have indications for Doppler study: Past obstetric history, abnormal uterine artery Doppler, referral for second opinion Uncomplicated pregnancy with term delivery of an appropriately growth baby Exclusion criteria Abdominal circumference <5 th percentile Significant maternal medical conditions Known fetal abnormality Gestation age range wks gestation22-42 wks gestation UA PI range 1.69 – – 1.40 Authors Arduni et al Acharya et al Merz et al Published journal J Perinat MedAJOG Ultrasonography in ObGyn Year of publication Study number Cohort population Uncomplicated pregnancies Uncomplicated singleton pregnancies - Exclusion criteria Pregnancy induced hypertension Fetal growth restriction Gestation diabetes Gestation age range wks gestation wks gestation wks gestation UA PI range 2.03 – Results