OC24.01: Doppler cardiotocography and biophysical profile

Abstract

Fetal surveillance aims to predict or detect fetal compromise. Ideally this is achieved early enough to institute management in order to avert irreparable damage and improve outcome. Development of hypoxemia and acidemia are the most important prenatally detectable causes of fetal compromise. Examination of fetal cardiovascular and behavioral responses is the primary means to document this progression. In order to provide the best disease specific application of prenatal monitoring modalities it is necessary to understand their relationship to fetal status. In the fetus with an anatomically normal central nervous system fetal tone, movement, heart rate variability and heart rate variation are most closely related to acute changes in oxygenation. Fetal breathing and cerebral blood flow dynamics are examples of parameters that are dependent on additional factors (glucose concentration and blood pressure respectively). Other variables are surrogate markers for impaired oxygenation. These include umbilical artery Doppler (primarily related to placental blood flow resistance), venous Doppler parameters (related to forward cardiac function) and amniotic fluid volume (related to renal plasma flow). Because these testing variables are affected at different severities of acid-base derangement they can be used to estimate the risk for fetal compromise. Elevations of placental blood flow resistance (uterine and umbilical artery Doppler indices) are early markers of placental dysfunction. Brain sparing, loss of fetal breathing and loss of fetal heart rate reactivity are intermediate findings that indicate the need for more detailed assessment. Absence, or reversal of umbilical artery end-diastolic velocity, elevation of venous Doppler indices indicate advance to decompensation. Absence or reversal of the ductus venosus a-wave, decrease of computerized short term variation below 3.5 msec, loss of fetal movement and tone are late signs of fetal compromise that often precede stillbirth. How the timing and form of intervention for these different stages of compromise are critically influenced by gestational age remains to be determined for many fetal conditions through randomized controlled trials that are underway.