Intrapartum fetal monitoring:: its basis and current developments

When electronic fetal heart rate recorders were introduced 30 years ago, obstetricians hoped to prevent the delivery of dead or impaired babies who had suffered from birth asphyxia. We now realize that the cardiotocogram (CTG) does not provide all the information required to achieve this. Today, it is possible to improve our ability to interpret the fetal response to the stress of labor by a more thorough analysis of acid-base status and the fetal electrocardiogram (ECG). What information are we looking for? For the purposes of intrapartum monitoring, there are three groups of fetuses that we should be able to identify: the fetus that is untroubled by the events of labor; the fetus that is troubled but able to compensate fully and is in no immediate danger; and the fetus that is troubled and utilizing key resources in an attempt to compensate or is unable to compensate fully. This is the group that may benefit from appropriately timed intervention. The capacity of fetuses to handle hypoxemia may differ greatly, depending on the situation prior to the hypoxic event. Therefore, it may be difficult to rely only on the level of oxygenation. It might be more rewarding to try to interpret the reactions taking place in a high-priority organ such as the heart or the brain. After decades of dedicated research and development, ST waveform analysis has emerged as a new tool to assist in the interpretation of ominous CTG patterns. The new STAN(R) monitor with its strict guidelines and computer-assisted interpretation of the ECG has been shown to have a diagnostic capacity for identifying fetuses with significant intrapartum asphyxia. On these grounds, it should be possible to reduce the threat of asphyxia.