The ratio of fetal heart rate accelerations with fetal movements to total fetal movements in normal and growth-retarded fetuses

Objective: The ratio of fetal heart rate accelerations with fetal movements to total fetal movements (FMAc/FM) increases with advancing gestation, and has been related to advancing maturity of the fetal nervous system. In growth-retarded fetuses, pulmonary maturation is thought to be accelerated. In this study we have examined the FMAc/FM in growth-retarded fetuses in an attempt to see if the maturation of the fetal nervous system, as indicated by the FMAc/FM, is similarly accelerated. Methods: Nonstress tests were performed in 69 pregnancies complicated by growth retardation, and 80 normal control pregnancies. For each group, a straight line representing the mean weekly percent ratio of the FMAc/FM was constructed and compared. Linear regression analysis of variance and t test were used for the statistical analysis. Results: In both groups, the FMAc/FM increased significantly throughout gestation. The rate of increase was similar in both groups. Conclusions: Growth-retarded fetuses cannot be differentiated from normal controls by the rate of increase of FMAc/FM throughout gestation. Possibly, their rate of nervous system maturation is not accelerated, or alternately, the FMAc/FM index is not sensitive enough to monitor such changes.