The effect of vibro-acoustic stimulation on fetal behavioral state organization.

During the third trimester of pregnancy there is a gradual development of fetal behavioral states. These states are distinct and discontinuous modes of neural activity; they reflect a certain degree of maturity and/or integrity of the fetal brain and are homologous with those seen in newborn infants. Abnormal state development has been found in growth retarded fetuses and in fetuses of women with type-1 diabetes. Behavioral state organization is not easily influenced by external factors and most stimuli fail to induce a state change when the fetus is in quiet sleep (state 1F). However, fetuses do react to vibro-acoustic stimulation (VAS) with an electronic artificial larynx. This stimulus induces excessive fetal movements, prolonged tachycardia, disorganization of behavioral states, and state transitions normally not seen in healthy fetuses. The backgrounds for these excessive and unusual reactions are largely unknown. For the time being, it seems better not to use this device in clinical practice. In this review paper, data on the development of behavioral states and on fetal reactions to VAS are discussed.