From the Guidelines
Late decelerations in fetal heart rate monitoring are characterized by a gradual decrease in heart rate that begins after the onset of a contraction and returns to baseline after the contraction ends, indicating uteroplacental insufficiency. The criteria for identifying late decelerations include:
- a gradual decrease in fetal heart rate (taking more than 30 seconds from onset to nadir)
- onset occurring after the peak of the contraction
- nadir of the deceleration occurring after the peak of the contraction
- and a gradual return to baseline 1. These decelerations are concerning because they typically indicate uteroplacental insufficiency, and their presence warrants immediate attention, especially when accompanied by minimal variability. Some key points to consider when identifying late decelerations include:
- The depth of the deceleration is less important than its timing relative to contractions and its repetitive nature
- Persistent late decelerations are particularly concerning and warrant immediate attention
- When late decelerations are identified, interventions should focus on improving uteroplacental perfusion, including maternal position changes (usually left lateral), oxygen administration, IV fluid bolus, discontinuation of oxytocin if being used, and treating maternal hypotension if present 1. If these measures don't resolve the pattern and fetal compromise is suspected, expedited delivery may be necessary, as late decelerations reflect a situation where the fetus cannot maintain normal oxygenation during contractions due to compromised placental function, making them an important warning sign of potential fetal hypoxia 1.
From the Research
Late Decel Criteria
The provided studies do not directly address late decel criteria. However, they discuss various aspects of fetal distress and intrauterine resuscitation, which may be related to late decelerations in fetal heart rate tracings.
- Fetal heart rate monitoring is used as a screening technique to define a population at significant risk for fetal acidosis 2.
- Intrauterine resuscitation techniques, such as discontinuing oxytocin, correcting maternal hypotension, administering oxygen to the mother, and alleviating cord compression, can help improve fetal oxygenation 2.
- Terbutaline, a beta-2 adrenergic receptor stimulator, has been used to decrease myometrial activity and improve uteroplacental blood flow in patients with acute intrapartum fetal distress 3, 4.
- Maternal oxygen therapy is often used as a first-line measure for intrauterine resuscitation, but recent evidence suggests potential risks to the mother and fetus or newborn, and its use should be reserved after other measures have been unsuccessful 5.
- Terbutaline has been shown to improve fetal heart rate tracings and pH in patients with acute intrapartum fetal distress 3, 6.