CASE 2 EFM tracings belie the clinical situation
A 20-year-old woman (G1P0) presented for induction of labor at 41 weeks’ gestation. Continuous EFM recording was initiated, and the patient was given dinoprostone and, subsequently, oxytocin. Rupture of membranes at 3 cm demonstrated a small amount of fluid with thick meconium. The patient progressed to complete dilation and developed a temperature of 38.5°C; the EFM baseline increased to 180 BPM. Throughout the first hour of the second stage of labor, the EFM demonstrated breaks in the tracing and a heart rate of 130 to 150 BPM with each pushing effort (FIGURE 2A). The Doppler monitor was subsequently adjusted to focus on the fetal heart and repetitive late decelerations were observed (FIGURE 2B). An emergent cesarean delivery was performed. A depressed newborn male was delivered, with Apgar scores of 2 and 4 at 1 and 5 minutes, respectively, and significant metabolic acidosis.
What happened?
This EFM recording during the second stage of labor shows pushing efforts every 2 minutes (panel A). With adjustment of the Doppler monitor, the pattern of late decelerations is visible (panel B).
Abbreviation: EFM, electronic fetal heart rate monitoring
Fetal versus maternal responses to pushing
The fetal variable deceleration pattern is well recognized by clinicians. As a result of umbilical cord occlusion (due to compression, stretching, or twisting of the cord), fetal variable decelerations have a typical pattern. An initial acceleration shoulder resulting from umbilical vein occlusion (due to reduced venous return) is followed by an umbilical artery occlusion–induced sharp deceleration. The relief of the occlusion allows the sharp return toward baseline with the secondary shoulder overshoot.
In some cases, partial umbilical cord occlusion that affects only the fetal umbilical vein may result in an acceleration, although these usually resolve or evolve into variable decelerations within 30 minutes. By contrast, the maternal heart rate typically increases with contractions and with maternal pushing efforts. Thus, a repetitive pattern of heart rate accelerations with each contraction should warn of a possible maternal heart rate recording.
How maternal heart rate responds to pushing. Maternal pushing is a Valsalva maneuver. Although there are 4 classic cardiovascular phases of Valsalva responses, the typical maternal pushing effort results in an increase in the maternal heart rate. With the common sequence of three 10-second pushes during each contraction, the maternal heart rate often exhibits 3 acceleration and deceleration responses. The maternal heart rate tracing looks similar to the shape of the Three Sisters mountain peaks in Oregon (FIGURE 3). Due to Valsalva physiology, the 3 peaks of the Sisters mirror the 3 uterine wave form peaks, although with a 5- to 10-second delay in the heart rate responses (mountain peaks) from the pushing efforts.
The shape of the Three Sisters mountain peaks is similar to the pattern of maternal heart rate (red line) in response to 3 maternal pushing efforts during a single uterine contraction (yellow line).
Pre- and postcontraction changes offer clues. Several classic findings aid in differentiating the maternal from the fetal heart rate. If the tracing is maternal, typically the heart rate gradually decreases following the end of the contraction/pushing and continues to decrease until the start of the next contraction/pushing, at which time it increases. During the push, the Three Sisters wave form, with the 5- to 10-second offset, should alert the clinician to possible maternal heart rate recordings. By contrast, the fetal heart rate variable deceleration typically increases following the end of the maternal contraction/pushing and is either stable or increases further (variable with slow recovery) prior to the next uterine contraction/pushing effort. These differences in the patterns of precontraction and postcontraction changes can be very valuable in differentiating periods of maternal versus fetal heart rate recordings.
With “slipping” between fetal and maternal recording, it is not uncommon to record fetal heart rate between contractions, slip to the maternal heart rate during the pushing effort, and return again to the fetal heart rate with the end of the contraction. When confounded with the potential for other EFM artifacts, including doubling of a low maternal or fetal heart rate, or halving of a tachycardic signal, it is not surprising that it is challenging to recognize an EFM maternal heart rate recording.
CASE 2 Check the monitor for accurate focus
A retrospective analysis of this case revealed that the maternal heart rate was recorded with each contraction throughout the second stage. The actual fetal heart rate pattern of decelerations was revealed with the refocusing of the Doppler monitor.
Read how subtle slipping manifested in the EFM tracing of Case 3