Quantitative analysis of fetal general movements: methodological considerations

Objectives: We studied the effects of gestational age and various smoothing procedures on four incidence parameters of fetal general movement, to eval uate reported variation in previous studies and to establish the optimal wa y of smoothing. Subjects and methods: General movements were studied longit udinally between 24 and 40 weeks of gestation in 29 healthy fetuses. The nu mber of movement bursts per hour, burst duration, onset-onset interval betw een successive bursts (OOI) and the percentage incidence were analysed in d etail. Results: Advancing gestation was characterised by a proportional inc rease in OOI's lasting >60 s and a decreased number of bursts, whereas burs t duration remained relatively stable (unsmoothed data). Smoothing resulted in an exaggerated decrease in the number of bursts and in increases in bur st duration, OOI and percentage incidence. These changes occurred in a gest ational age specific manner and could largely explain the variation in resu lts between previous studies. Conclusions: The temporal patterning of fetal general movements undergoes developmental change, as shown by differential effects of smoothing between mid and late pregnancy. A smoothing procedure is to be preferred which includes short intervals (1-3 s) between the elem ents composing a burst, since small changes in movement generation can stil l be recognised this way. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.