Objective : To evaluate the validity of systolic/diastolic (S/D) ratio of the umbilical artery in predicting intrauterine growth restriction (IUGR).
Study Design : Diagnostic test study.
Setting : Maharaj Nakorn Chiang Mai Hospital, Chiang Mai University.
Subjects : Two hundred and twelve singleton pregnancies between 30 and 42 weeks’ gestation with clinical suspicion of IUGR were recruited and followed-up between December 1st 1995 and June 30th 1998. They were sonographically examined for routine fetal biometry and S/D ratio of umbilical artery Doppler waveform measurement within 14 days of delivery. All of them had an accurate date of last menstrual period and were
between 30-42 weeks’ gestation.
Material and Method : The umbilical artery S/D ratio was obtained by the same experienced sonographer, using the same ultrasound machine, Aloka 680EX, (Tokyo, Japan). The S/D ratio of 3 or greater was considered abnormal, predicting IUGR prenatally for every gestational week. IUGR was defined as low birth weight of less than the 10th percentile of the standard birth weight curve of Maharaj Nakorn Chiang Mai Hospital.
Main Outcome Measures : sensitivity, specificity, positive predictive value and negative predictive value.
Results : The prevalence of IUGR among the study group was 50.9%. The S/D ratio of 3 or greater for predicting of IUGR gave the sensitivity, specificity, positive predictive value, and negative predictive value of 52.96%, 78.85%, 74.42% and 65.08%, respectively.
Conclusion : The umbilical artery S/D ratio has relatively low sensitivity and is not a suitable test for IUGR screening. However, the specificity is rather high and it may be helpful in combination with other parameters.

Keywords : Doppler waveform index, Umbilical artery, S/D ratio, Intrauterine growth restriction, Detection