Situation: A 28-year-old woman at 40 weeks' gestation, who had one previous term vaginal birth, is in the second stage of labor at a lying-in clinic that follows the Department of Health (DOH) Essential Intrapartum and Newborn Care (EINC) protocol. Her first stage was uncomplicated, and the fetus is in a vertex presentation. During pushing, the nurse auscultates the fetal heart rate (FHR) with a handheld Doppler, counting for 60 seconds right after each of three consecutive contractions, and palpates the mother's radial pulse at the same moments: Check 1: Doppler 150 beats/min; maternal pulse 88/min Check 2: Doppler 92 beats/min; maternal pulse 90/min Check 3: Doppler 148 beats/min; maternal pulse 86/min Which interpretation of these readings is MOST accurate?

Checks 1 and 3 show a fetal rate within the normal 110 to 160 beats/min, clearly distinct from the mother's pulse. The single low count at check 2 is almost identical to the maternal pulse taken at the same moment, which is typical of picking up the maternal signal, a common error during pushing in the second stage. The nurse confirms by listening again over the fetal back while palpating the mother's pulse, rather than averaging the counts or labeling a deceleration.

During the second stage of labor, the fetal heart rate is assessed immediately after a contraction because that is when the fetal signal is most audible and the risk of confusing it with maternal structures is highest. In this scenario, checks 1 and 3 produced rates of 150 beats/min and 148 beats/min, both within the normal baseline range of 110 to 160 beats/min and clearly separate from the maternal radial pulse of 88/min and 86/min. The isolated reading at check 2, 92 beats/min, is almost identical to the simultaneously palpated maternal pulse of 90/min. This pattern is the classic signature of maternal heart rate capture rather than a true fetal rhythm change.

The physiologic basis for this interpretation rests on what is actually being heard through a handheld Doppler. A Doppler device detects motion from any pulsatile structure within its ultrasound beam. During the second stage, the fetus descends, rotates, and is compressed by maternal soft tissue and the bony pelvis. The maternal aorta, iliac vessels, and uterine arteries lie in close proximity to the fetal back and chest. When the examiner angles the probe slightly or the fetus shifts position, the dominant reflected signal can switch from the fetal heart to a maternal vessel. Because the maternal heart rate in a healthy laboring woman is typically 80 to 100 beats/min, a sudden drop from the 140s to 150s down to the 90s—matching the mother’s radial pulse—is far more likely to represent signal confusion than a genuine fetal bradycardia.

A true fetal bradycardia would not resolve spontaneously within one contraction cycle without a preceding deceleration pattern, and it would not align so precisely with the maternal pulse. Early decelerations caused by head compression mirror the contraction waveform and return to baseline by the end of the contraction, but they do not drop to 92 beats/min in an otherwise uncomplicated vertex presentation with a previously normal baseline. Similarly, averaging the three counts to arrive at a baseline of 130 beats/min is statistically appealing but clinically misleading, because it treats an artifact as a real data point.

The EINC protocol emphasizes intermittent auscultation with a handheld Doppler as the standard for low-risk labor, but it also requires that the nurse differentiate fetal from maternal signals. The correct response is not to label a deceleration or recalculate a baseline, but to reposition the Doppler over the fetal back while simultaneously palpating the maternal radial pulse and recheck the FHR. If the new count remains in the 110 to 160 beats/min range and is clearly distinct from the maternal pulse, the isolated low reading is confirmed as artifact.

The evidence base supports this concern. A prospective study comparing trans-abdominal fetal ECG with Doppler telemetry found that confusion between fetal and maternal heart rates occurred at a significantly higher rate with Doppler telemetry during the second stage of labor ^[1]. The mechanical forces of descent and maternal vessel proximity make this period uniquely vulnerable to signal crossover. Another study comparing abdominal fetal ECG with external Doppler CTG reported that Doppler signal quality deteriorates specifically in the second stage, further increasing the likelihood of capturing maternal pulsations ^[4]. Consensus guidelines for intermittent auscultation in community birth settings and in low-resource settings both identify handheld Doppler as the preferred tool but emphasize the need for simultaneous maternal pulse palpation to detect exactly this type of error .

Reading	Doppler rate	Maternal pulse	Interpretation
Check 1	150 beats/min	88/min	Fetal signal, normal baseline
Check 2	92 beats/min	90/min	Maternal pulse captured, artifact
Check 3	148 beats/min	86/min	Fetal signal, normal baseline

Watch out! A single low Doppler reading that matches the maternal radial pulse is not a fetal bradycardia until proven otherwise. Key point! During the second stage, always auscultate the FHR while palpating the mother’s pulse at the same moment; if the two are identical or nearly identical, suspect maternal signal capture and recheck after repositioning the Doppler over the fetal back.