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Computerized measurement of heart rate variation in fetal anemia caused by rhesus alloimmunization
D L Economides1, M Selinger, J Ferguson
1Nuffield Department of Obstetrics and Gynaecology, University of Oxford, John Radcliffe Hospital, England.
Objective:
The purpose of this study was to examine the relationship between fetal heart rate variation and fetal hematocrit.
Study Design:
In 36 red-cell alloimmunized pregnancies (mean gestational age 30, range 25 to 36 weeks) 65 computerized fetal heart rate recordings were obtained before ultrasonographically guided fetal blood sampling for the measurement of fetal hematocrit. The recordings were captured and analyzed by a microcomputer on-line. Fetal heart rate variation in anemic fetuses was accurately measured.
Results:
Significant positive correlations between short-term or long-term heart rate variation and fetal hematocrit have been demonstrated even after adjusting for the effect of gestation (r = 0.60, n = 65, p less than 0.01, y = 19.264 + 0.913x - 0.003x2; r = 0.52, n = 65, p less than 0.01, y = 21.13 + 0.858x - 0.003x2, respectively). The relationship was best described by a quadratic model. When short-term variation was less than 5 milliseconds or long-term variation was less than 30 milliseconds, the positive predictive values for fetal hematocrit of less than 30 were 85% and 90%, and the negative predictive values 56% and 57%, respectively.
Conclusion:
Computerized recording and analysis of fetal heart rate variation may prove to be a useful noninvasive tool for assessing fetal anemia in red-cell alloimmunization.