Objectives: (1) to assess the relationship of basal fetal heart rate (FHR) with both long term (LTV) and short term (STV) FHR variation in low-risk pregnancies, longitudinally from 24 weeks gestation onwards and (2) to investigate the relationship of FHR with LTV and STV in intrauterine growth retarded (IUGR) fetuses.
Study design: Computerised FHR recordings were made in twenty-nine uncomplicated pregnancies (n=224) and in twenty-seven IUGR fetuses who were selected retrospectively from three databases (n=135). Nomograms of FHR variation with FHR and GA were constructed using multilevel analysis.
Results and conclusions: There was a strong negative relationship of FHR with both LTV and STV in the control group (R2=53% and 52%, respectively). In the IUGR fetuses, FHR was generally higher than in normal fetuses whereas LTV and STV were lower. The relationship of FHR with LTV and STV in the IUGR group was less strong (for both: R2=18%). Correction of FHR variation for basal FHR in the IUGR fetuses only resulted in a slight reduction in the number of recordings with a variation below the normal range. As it does not improve the recognition of fetuses being considered at the highest risk, such a correction of FHR variation for basal FHR is therefore not necessary. Intrafetal consistency, known to be present in healthy fetuses, was also present in the IUGR fetuses with a low FHR variation.