HEART-RATE VARIATION DURING FETAL BEHAVIORAL STATE-1 AND STATE-2

Fetal heart rate (FHR) variation was numerically assessed in relation to behavioural states in 34 normal near term fetuses, in order to stud y the normal ranges of FHR variation during state 1F and 2F and to det ermine possible factors influencing variation in these states. In all individuals 2-h recordings were made of fetal heart rate, and body and eye movements. FHR variation was quantified using the Sonicaid System 8000(R). During both 1F and 2F there was a large range in variation, with a wide overlap in variation between both states (mean 1-min range in pulse intervals 16-53 ms and 36-97 ms, respectively). In all fetus es variation was higher during 2F than during 1F. The large ranges in variation were mainly caused by differences in basal heart rate and th e correlation coefficients between rate (beats/min) and variation were -0.68 and -0.49 for IF and 2F, respectively. Other reasons for a rela tively high FHR variation during IF included 'pseudo' sinusoidal patte rns related to fetal sucking or mouth movements and relatively flat pe riods sporadically interrupted by an acceleration. With the System 800 0, periods of low and high variation are identified using fixed criter ia. Because of the large overlap in variation between both states, the se episodes poorly correlated with the underlying behavioural states. Objective identification of the heart rate patterns during states IF a nd 2F requires incorporation of heart rate itself in the analysis. As yet, 'global' visual identification of heart rate patterns is superior to computer analysis in identifying the underlying fetal behavioural states.