Using S/D ratios to predict fetal outcome

Abstract

The systolic/diastolic (S/D) ratio is a measurement of the umbilical cord artery that compares the systolic with the diastolic flow and identifies the amount of resistance in the placental vasculature. This retrospective study made a direct comparison between the S/D ratios of third-trimester fetuses and their birth weights. Previous studies have reported fetuses with S/D ratios greater than 3.0, after 30 gestational weeks, to be at an increased risk for low birth weight. This study looked at outcomes of fetuses with S/D ratios greater than 3.0, and ratios less than 3.0. One hundred S/D ratios were obtained and divided into three categories: less than 2.0, between 2.0 and 3.0, and greater than 3.0. The collected data showed 35.5% of low-birth-weight neonates had S/D ratios greater than 3.0. Those patients with S/D ratios less than 2.0 had the largest percentage (37.5%) of neonates above the 50th percentile in weight, whereas ratios between 2.0 and 3.0 had the highest percentage (59.46%) of neonates between the 11th and 50th weight percentiles. The S/D ratio is easily obtained and provides important information in conjunction with fetal structural measurements when predicting the outcome of a fetus.