The relationship between the response to external light stimulation and behavioral states in the human fetus: how it differs from vibroacoustic stimulation

Objective: To determine the effects of external light stimulation on fetal behavioral states and know the difference from those of vibroacoustic stimulation. Methods: A flashlight and a vibroacoustic stimulator was applied directly on the maternal abdomen to determine the response of 56 normal fetuses at 36-40 weeks gestation. Fetal heart rate (FHR) and body movements were recorded using an actocardiograph. and fetal eye movements were observed using real-time ultrasonography. Using Nijhuis's criteria, the fetal behavioral states (1F-4F) were determined. FHR acceleration was considered a fetal response to the stimulations. Results: The lag time between stimulation and fetal response was within 4 s. A positive response rate to the light stimulation was higher at behavioral states 2F (82%) and 3F (83%) than at state 1F (4%). Light stimulation changed the behavioral state of two of the six 3F fetuses (33%) from 3F to 4F. No change of state was observed in fetuses that were in states 1F and 2F. For vibroacoustic stimulation, fetal response was 100% positive and changes of states were observed frequently irrespective of the behavioral state before the stimulation. Conclusion: Fetal response to light stimulation is closely connected to fetal behavioral states and may reflect some distinct stages of the sleep-wakefulness cycle. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.