Clinical significance of fetal heart rate patterns during labor: IV. Agonal patterns

Abstract

The characteristics of fetal heart rate (FHR) patterns were reviewed in 11 cases where the infants died either intrapartum or within eight hours of birth as a consequence of distress during labor without prior recovery. The neonatal charts and the autopsy reports were also reviewed. The infants were grouped according to gestational age as premature (four), term (four), and postmature (three). Similarities and differences were studied in an attempt to delineate some common underlying factors. The premature fetuses have an extraordinary capacity to withstand clinical signs of severe distress (late deceleration and fixed and tachycardic base line) for many hours until the very moment of death and rarely pass meconium. The term fetuses can withstand less prolonged periods of severe distress, the fixed FHR base line and impressive decelerations preceding immediate death; they consistently passed meconium, three of four had aspirated meconium. All of the postterm fetuses had massive meconium aspiration, but the FHR patterns had a bizarre appearance; several hours before death some late decelerations were followed by tachycardia and fixed base lines but no decelerations. Subsequent occurrence of erratic severe decelerations immediately preceded sudden death. Possible reasons for these different pathophysiologic responses are discussed. In the study of FHR tracings, a variable of utmost importance is chronologic age of gestation. Its value cannot be overemphasized for an accurate interpretation of the fetal condition and good decisions for management.