The physiological basis for fetal assessment.

Remarkable progress has been made during the last 15 years in understanding mechanisms that occur in the fetus as a response to hypoxia. Human experiments have defined the normal patterns and responses of the fetus to changes in the maternal environment. Considerable data exist regarding patterns of fetal breathing and body movements and of the FHR during midpregnancy in humans. Unfortunately, very little data exist from animal experiments during midpregnancy to confirm the usefulness of indices of fetal activity and blood flow during this important time in gestation. At the present time, it is sensible to conclude that a scientific basis exists for the application of fetal testing methods such as the biophysical profile, NST, and arterial wave-form velocities during the last 10 weeks of human pregnancy. However, it is important to recognize that the scientific basis for the use of such tests does not exist from animal experiments during the important period of 0.5 to 0.75 of gestation. As a result, clinicians need to be cautious regarding the interpretation of measurements made between 20 and 30 weeks' gestation. At present, fetal tests are based on observation of normal fetal behavior. The methods are time-consuming, labor-intensive, and subject to error because of the periodicities in fetal activity. The purpose of this symposium is to consider whether measurement of fetal responses to sound and vibration might be a more effective method of assessing fetal health. It is to be hoped that such new methods will be vigorously investigated before introduction into clinical practice.