Observations of biophysical activities in the normal fetus

Biophysical activities such as FBM, GBM, and accelerations in the healthy human fetus near term occur episodically in keeping with the development of behavioral states in utero. It is therefore important to allow for the normal rest-activity cycles of healthy fetuses when designing clinical strategies for the surveillance of fetal health during the antepartum period. Diurnal rhythms are present in the incidence of FBM and GBM, as well as in mean FHR. These appear to be related to intact maternal or fetal adrenal gland function. The incidence and amplitude of FBM are strongly influenced by maternal meals, and therefore by plasma glucose concentrations, whereas maternal meals have no effect on GBM or FHR accelerations. The association of FHR accelerations with GBM becomes stronger with advancing gestational age such that near term close to 90 per cent of accelerations occur with movement. Younger fetuses move overall approximately the same amount of time as term fetuses, although the movements are more frequent and of a shorter duration. Maternal smoking, and alcohol and drug ingestion all affect FBM, GBM, and FHR to various extents, underlining the importance of documenting the prior maternal use of these substances when using biophysical activities to assess fetal health in the antepartum period.