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Definitions
Antepartum fetal testing: a compilation of methods devised to differentiate normal from compromised fetuses prior to the onset of labor. These methods may be based on endocrine markers in maternal serum, Doppler-ultrasound-based continuous fetal heart rate monitoring, and real-time ultrasound evaluation of fetal biophysical variables and amniotic fluid volume.
Fetal biophysical profile score: a score derived from observation of 4 discrete dynamic fetal biophysical variables (heart rate acceleration in response to fetal movement [nonstress test or NST], fetal breathing, gross body movement, tone) and one static variable (amniotic fluid volume). The score can range from 10/10 (all variables normal) to 0/10 (all variables abnormal). The method is highly accurate in differentiating healthy from compromised fetuses.
Perinatal asphyxia: a collective term describing the fetus, who in response to exposure to either hypoxia or ischemia, exhibits hypoxemia and a metabolic academia (abnormal base deficit). Perinatal asphyxia may be acute or chronic. The fetal adaptive response to perinatal asphyxia forms the basis for the evaluation of fetal dynamic biophysical variables and amniotic fluid volume. Perinatal asphyxia is a recognized cause of perinatal death and morbidities such as cerebral palsy among affected surviving perinates.
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The development of objective clinical methods for the detection of the fetus at risk for death or damage in utero began in earnest only in the past few decades. The initial forays were in the measurement of endocrine products released by the placenta into the maternal circulation. A wide range of compounds, including placental enzymes (alkaline phosphatase, leucine amino-peptidase), placental-specific hormones (placental lactogen), and placental conversion products (estriols, estetrol) were studied. For most there was a relation to fetal outcome, but none of these measures had the necessary accuracy to become a useful adjunct to clinical management. In the early 1960s, 2 clinical investigative teams, one headed by Hon in Yale and the other by Caldero-Barcia in Uruguay, reported methods for continuous recording of the fetal heart rate.1,2 This innovation ushered in the contemporary era of fetal evaluation based on dynamic biophysical monitoring. Although designed for the intrapartum period, the application of heart rate monitoring in the antepartum period was quickly realized, and a generation of tests based on heart rate responses to contractions (the contraction stress test), fetal movements (the nonstress test [NST]), or both came into vogue3 and quickly supplanted the biochemical tests. In the late 1960s, 2 groups, those of Dawes in Oxford and Tchobroutsky in Paris, reported fetal breathing movements as a normal characteristic of intrauterine life.3,4 Dawes et al in a series of elegant experiments in the chronic fetal lamb preparation were able to demonstrate an exquisite sensitivity of the fetal respiratory center to experimental hypoxemia,5 thereby creating interest in the potential of this measurement in predicting human fetal compromise. The clinical application of these observations was thwarted by the inability to record human fetal breathing accurately.
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