Fetal heart rate patterns in the small-for-gestational-age human fetus

A total of 24 pregnant women with growth-retarded fetuses were studied to examine the distribution of fetal heart rate accelerations between 30 and 40 weeks' gestation, as compared with those of fetuses of normal growth that were matched for gestational age and length of fetal heart rate tracings. Growth-retarded fetuses had significantly lower PO2 levels in the umbilical artery at birth (3 mm Hg less) than did healthy fetuses (p less than 0.05), but without metabolic acidosis. There was a larger proportion of small amplitude (less than 10 beats/min) and a smaller proportion of large amplitude (greater than 20 beats/min) fetal heart rate accelerations in the small-for-gestational-age fetuses than in the fetuses of normal growth. Although the number of accelerations was significantly reduced (50% less) in growth-retarded fetuses compared with healthy fetuses, there was no significant difference in the mean basal fetal heart rate and the mean number of decelerations between the two groups. Currently used definition of an acceleration as greater than or equal to 15 beats/min for greater than or equal to 15 seconds was applicable only in fetuses of normal growth. We hypothesized that a decrease in absolute acceleration frequency might be a useful index to detect the chronically hypoxemic fetus before severe metabolic acidosis and irreversible damage occurred.