Chapter 184 Antepartum Fetal Testing
THE CHALLENGE
Scope of the Problem: There are roughly 15 fetal or neonatal deaths for every 1000 births in the United States.
Objectives of Management: To identify those fetuses at high risk and those whose status is deteriorating or nonreassuring so that intervention can take place to prevent mortality. Ultimately, the reduction of fetal morbidity and the improvement of neurologic outcome would be ideal as well, but objective studies to support the effectiveness of antepartum fetal testing are lacking.
TACTICS
Relevant Pathophysiology: The nonstress test (NST) and contraction stress test (CST) are based on the premise that when fetal oxygenation is only marginally adequate, the fetus will not possess the normal ability to modulate heart rate in response to fetal movement or to tolerate the stress of placental ischemia induced by uterine contractions. A normal (reactive) NST has two or more accelerations (15 beats/min for 15 seconds) in a 20-minute period. Acoustic stimulation may also be used to startle the fetus and induce a heart rate increase. In the CST, the occurrence of late decelerations occurring with 50% or more contractions (regardless of frequency) is “positive” and suggests fetal risk. The biophysical profile (BPP) is based on the NST, augmented by measures of fetal breathing movements, fetal activity and tone, and quantitation of amniotic fluid volume rated on a 10-point scale (normal: 8–10/10, equivocal: 6/10, abnormal: ≤5/10). The pulsatile character of fetal blood flow in the umbilical cord or the middle cerebral artery may be used to assess the health of high-risk pregnancies, but these tests require special expertise to both perform and interpret.
