The STAN™ method
Oxygen deficiency during delivery is a known cause of neurological damage resulting in lifelong sequelae. Intrapartum asphyxia resulting in neurological damage or perinatal death is rare, but the human, social and economic consequences of a damaged child are so severe that it justifies all efforts to identify fetuses at risk.
Recording the FHR and the uterine contractions has become standard practice in all developed countries. The FHR trace contains important information and provides a valuable insight into the condition of the fetus. A normal FHR tracing, with moderate variability and accelerations identifies a fetus that is fully capable of reacting to the stress of labor. A FHR with absent variability and reactivity identifies a fetus that is unable to respond. Together with the recording of the FHR, the fetal ECG waveform may provide additional information on the fetus’ condition during labor.
The STAN method is a combination of FHR interpretation and ST Analysis. ST Analysis is based on changes in the fetal ECG waveform determined by the myocardial adaptation to oxygen deficiency. It is the computerized real-time analysis of the ST interval of the fetal ECG.
ST Analysis is indicated as an adjunct to FHR monitoring to determine whether obstetrical intervention is warranted when there is increased risk of developing metabolic acidosis. The intended use is in patients with planned vaginal delivery, a term pregnancy of 36 or more completed gestational weeks, singleton fetus, vertex presentation and ruptured amniotic membranes.
For a complete list of the indications, contraindications, warnings and precautions, see here.
Two large-scale randomized controlled trials evaluating the STAN method have been conducted. The most recent trial(1) included 4966 term fetuses in three large labor wards in Sweden. After exclusion of inadequate recordings and fetuses with malformations the findings showed a 61 % decrease in the number of fetuses born with cord artery metabolic acidosis in the FHR+ST group, at the same time as a 28 % decrease in operative interventions due to fetal distress. The authors concluded that intrapartum monitoring with FHR combined with automatic ST waveform analysis increases the ability of the obstetrician to identify fetal hypoxia and to intervene more appropriately, resulting in an improved perinatal outcome.
A follow-up(2) of the Swedish randomized controlled trial evaluated the neonatal outcome with a focus on the complicated or adverse neonatal cases. The results showed a reduction in the incidence of newborn infants with marked neurological symptoms in the FHR+ST group. The authors concluded that the most important finding of the study was the prevalence of ST changes that are detected at an appropriate point in time to allow for earlier and more consistent intervention.
The first study(3) of ST Analysis in the USA in 2006 was a prospective, non-randomized study enrolling 530 patients from diverse populations and providers in six university and community medical centers. The results of the study demonstrated that the ST Analysis can be applied to support obstetric decision making and that unneeded interventions for non reassuring FHR can be safely avoided. The authors conclude that US clinicians can use the ST Analysis effectively and in a manner similar to that of experienced STAN users.
Please see more publications here.
(1) Amer-Wåhlin et al. Intrapartum Fetal Monitoring: Cardiotocography versus Cardiotocography plus ST Analysis of the Fetal ECG. A Swedish Randomized Controlled Trial. Lancet 2001;358:534-38.
(2) Norén et al. Fetal electrocardiography in labour and neonatal outcome: data from the Swedish randomised controlled trial on intrapartum fetal monitoring. Am J Obstet Gynecol. 2003;188:183-192.
(3) Devoe et al. United States multicenter clinical usage study of the STAN 21 electronic fetal monitoring system. Am J Obstet Gynecol. 2006;195:729–34.