Characterization of the reduced heart rate variation in growth-retarded fetuses.

Fetal heart rate (FHR) variation has been studied by computerized numerical analysis in 20 growth-retarded fetuses and 20 normal fetuses matched for gestational age. FHR variation was significantly reduced in the 14 growth-retarded fetuses where there was clinical evidence of associated pathology. Rest-activity cycles were assessed by changes in FHR variation and fetal movements. The growth-retarded fetuses with reduced FHR variation showed the same pattern of rest and activity as normal fetuses but the changes in FHR variation were of lower amplitude. This was observed even in the subgroup of six fetuses with the lowest FHR variation. Thus the unreactive FHR patterns associated with growth retardation do not arise because the fetus spends less time in activity.