T he purpose of this article is to study a system for antepartum fetal evaluation. The task is to investigate the Doppler ul- trasound measurements of the umbilical artery and the cerebral artery to relate the health status of a fetus by using discriminant functions of pattern recogni- tion. We then analyze the individual ef- fects of various blood-flow velocity waveforms using principal component analysis. Overview Antenatal care in recent years has under- gone a sea of changes. After each cause of maternal death was, one by one, elimi- nated, the focus of care shifted to the un- born baby. Obstetricians began to be concerned not only with prevention of mortality but also with the detection of fe- tal compromise and the timely delivery of such infants in an effort to enhance their future potentials. Antepartum heart rate tests such as the non stress test (NST) and the contraction stress test (CST) were used at most medi- cal centers [1, 2]. Specifically, the NST has proven to be an ideal screening test and remains the primary method for antepartum fetal evaluation. This test can be quickly performed in an outpatient set- ting and is easily interpreted. NST is counted to be among the best tests for antepartum evaluation. After 1977, Doppler ultrasound was ex- tensively used as a common diagnostic tool for antepartum risk assessment. Flow ve- locity waveform patterns in many fetal vessels have been studied [1, 2]. The um- bilical artery (UA) was the first and is the most studied artery. Adequate blood flow through the umbilical circulation is essen- tial to provide the fetus with oxygen and nutrients. In normal pregnancy, impedance to flow in the UA decreases with advanc- ing gestation, due to progressive matura- tion of the placenta and increase in the number of tertiary stem villi. Several stud- ies have already demonstrated the possibil- ities and limits of using umbilical Doppler for the assessment of fetal growth [1-8]. The most commonly used indices are: 1. Systolic/diastolic (S/D) ratio. 2. Resistance index (RI). 3. Pulsatility index (PI). where PI = (S/D)/mean velocity, and RI = (S/D)/D. These indices are defined by using the blood-flow velocity waveform. They are particularly useful in being independent of the angle between the ultrasound beam and the direction of blood flow. Various studies of intrauterine growth- retarded (IUGR) fetuses have shown that increased impedance to flow in the UA is associated with fetal hypoxemia and acidemia [1-4]. However, when these in- dices were used as a predictor of fetal well-being, only strong disturbances of the UA flow, such as absent end diastolic flow, were associated with acute fetal patency, but in this case it is still difficult to evaluate to degree of hypoxia and fetal distress. As a result, it becomes a neces- sity to improve the precision of diagnosis by the use of another flow velocity index. In response to prolonged fetal hypoxic stress, circulatory adaptation occurs, re- sulting in adjustment of the cardiac output to provide a constant oxygen supply to the fetal brain and other vital organs. In preg- 0739-5175/00/$10.00©2000IEEE 88 IEEE ENGINEERING IN MEDICINE AND BIOLOGY November/December 2000 Fikret Gurgen 1 , Nilgun Guler 2 , Fusun Varol 3 1 Computer Engineering Department, Bogazici University 2 Mathematical Engineering Department, Yildiz Technical University 3 Gynecology and Obstetrics Department, Trakya University ©1998 PhotoSpin, Inc. Studying the Umbilical Artery and Cerebral-Umbilical Ratio Using Discriminant Functions for Antepartum Fetal Evaluation