Fetal monitoring refers to any method used to track a baby’s heart rate and, in some cases, uterine contractions during pregnancy and labor. The most common form in hospitals today is electronic fetal monitoring (EFM), a technology that became commercially available in the early 1970s and quickly became standard practice in most developed countries.1PubMed. Social and professional influences of the technology of electronic fetal monitoring on obstetrical nursing Despite its near-universal use, the evidence behind continuous EFM is more complicated than many people realize, with well-documented tradeoffs between catching rare but serious problems and increasing the chance of surgical delivery.
How Electronic Fetal Monitoring Works
During labor, EFM tracks the baby’s heart rate alongside the mother’s contractions. In external monitoring, two sensors are strapped to the abdomen: one uses Doppler ultrasound to detect the fetal heartbeat, and the other measures the tightening of the uterine wall. Internal monitoring, used when a more precise reading is needed, involves placing a thin electrode directly on the baby’s scalp after the membranes have ruptured. Both approaches produce a continuous paper or digital tracing called a cardiotocograph (CTG), which clinicians read in real time.
The underlying logic is straightforward. A healthy fetus has a heart rate that speeds up and slows down in predictable ways. When the placenta delivers oxygen normally, you see a baseline rate that fluctuates moderately, with brief accelerations during fetal movement. When oxygen supply drops, the heart rate pattern changes. Late decelerations, for instance, are transient dips that begin after a contraction peaks and result from two overlapping mechanisms: a reflex triggered by oxygen-sensing receptors and direct depression of the heart muscle when oxygen runs low.2PubMed. Mechanisms of late decelerations of the fetal heart rate during hypoxia Recognizing these patterns is the entire point of the exercise: catch distress early enough to intervene before the baby is harmed.
Continuous EFM Versus Intermittent Listening
The alternative to continuous electronic monitoring is intermittent auscultation, where a clinician listens to the baby’s heartbeat at set intervals using a handheld Doppler device or a simple stethoscope-like instrument called a Pinard horn. This approach requires one-to-one nursing or midwifery care and has been standard in many low-risk settings around the world.
The largest body of trial evidence on the comparison comes from a Cochrane review that pooled multiple randomized controlled trials. Continuous EFM was associated with roughly a 50 percent reduction in neonatal seizures compared with intermittent auscultation, but that benefit came at a cost: cesarean deliveries increased by about 40 percent, and operative vaginal deliveries (forceps or vacuum) increased by about 20 percent.3Cochrane Database of Systematic Reviews. Routine electronic fetal monitoring during labor compared with intermittent auscultation: a randomized controlled trial There was no measurable difference in perinatal death or cerebral palsy between the two groups. That finding has shaped the debate ever since: continuous EFM appears to prevent a rare but serious short-term complication (seizures) while also substantially raising the odds of surgical birth, without clearly preventing the outcomes that matter most over a child’s lifetime.
A separate Cochrane review looked specifically at admission CTG, the common practice of running a short strip of monitoring when a woman first arrives in the labor ward. Women who received an admission CTG tended to end up on continuous monitoring more often during the rest of labor, and had roughly 20 percent higher rates of cesarean delivery, with no improvement in perinatal death rates.4Cochrane Database of Systematic Reviews. Admission cardiotocography versus intermittent auscultation of fetal heart rate on admission to labour ward for assessing fetal wellbeing In other words, the “just a quick check” strip at the door often cascades into more intervention without a clear benefit to the baby.
A scoping review examining the relationship between EFM and cesarean birth found that the largest observational study showed an 81 percent increased risk of primary cesarean when EFM was used in labor, though it did not separate high-risk from low-risk pregnancies.5PubMed. Electronic Fetal Monitoring and Cesarean Birth: A Scoping Review That nuance matters: for a pregnancy with known complications, the calculus is different from a straightforward low-risk labor.
The Interpretation Problem
One of the most persistent criticisms of EFM is that clinicians frequently disagree about what the tracings mean. The technology produces a continuous squiggle of data, and turning that squiggle into a clinical decision involves subjective judgment. Studies examining how well different observers agree on CTG readings have consistently found gaps, even when everyone is using the same classification system.
A study evaluating the 2015 FIGO guidelines for intrapartum monitoring found good agreement on some individual features of the tracing, like baseline heart rate and the presence of decelerations, but much weaker agreement on others, including reduced variability and late decelerations. When it came to classifying the overall tracing as normal, suspicious, or pathologic, agreement dropped further: observers matched on the overall category only about 60 percent of the time.6PubMed. Interobserver agreement in CTG interpretation using the 2015 FIGO guidelines for intrapartum fetal monitoring For “suspicious” tracings specifically, agreement was barely above coin-flip levels.
The picture gets worse when real stakes are involved. A study of obstetric experts reviewing abnormal heart rate tracings in the context of legal proceedings found that interobserver agreement was low, with kappa values between 0.11 and 0.18 for interpretation of the tracing itself.7PubMed. Intra- and interobserver agreement among obstetric experts in court regarding the review of abnormal fetal heart rate tracings and obstetrical management Even the same expert reviewing the same tracing on two different occasions agreed with themselves only about half the time. This is a technology whose tracings end up as central evidence in malpractice lawsuits, yet the experts testifying about those tracings can barely agree on what they show.
Classification Systems and What the Categories Actually Predict
In the United States, the standard approach uses a three-tier system. Category I tracings look normal and are considered reassuring. Category III tracings are clearly abnormal and call for immediate action. Category II is everything in between, and it is by far the most common classification during labor, which is part of the problem: an enormous bucket of “not normal but not definitively bad” tracings that clinicians must make real-time decisions about.
A systematic review and meta-analysis found that deliveries with Category II tracings had roughly 1.5 times the odds of a low five-minute Apgar score compared to Category I, and Category III tracings had about 14 times the odds.8PubMed. Three-tiered fetal heart rate interpretation system and adverse neonatal and maternal outcomes: a systematic review and meta-analysis For the most severe marker of acid-base disturbance, Category III tracings showed dramatically worse outcomes compared to both Category I and Category II. The three-tier system does stratify risk in a meaningful way, but the middle category remains so broad that it offers limited guidance for the clinician standing at the bedside.
Some researchers have proposed a five-tier system that divides that middle category into finer grades. A comparison of the two approaches found that the five-tier classification showed a closer relationship with cord blood gas values at delivery, suggesting it may be more useful for distinguishing which babies are actually in trouble from those who are simply showing benign variants.9PLoS ONE. Evaluation of 3-tier and 5-tier FHR pattern classifications using umbilical blood pH and base excess at delivery
Adjunct Tests When the Tracing Is Ambiguous
Because the CTG tracing alone has a high false-positive rate for fetal distress, clinicians have developed several backup tests to use when the strip looks worrying but the situation is unclear.
Fetal scalp blood sampling involves making a small nick on the baby’s scalp during labor and measuring the blood’s acidity. Traditionally this was done by measuring pH, but lactate measurement has gained ground because it requires a much smaller blood sample and is faster to perform. A randomized study found that the failure rate for the pH procedure was dramatically higher than for lactate measurement, with pH sampling about 16 times more likely to produce an unusable result.10PubMed. Lactate compared with pH analysis at fetal scalp blood sampling: a prospective randomised study A larger multicenter trial confirmed that outcomes were equivalent whether scalp blood was analyzed for pH or lactate, with no difference in rates of metabolic acidemia or operative delivery.11BMJ. Determination of pH or lactate in fetal scalp blood in management of intrapartum fetal distress: randomised controlled multicentre trial
A less invasive alternative is vibratory acoustic stimulation, where a small buzzing device is placed against the mother’s abdomen. The idea is that a healthy, well-oxygenated fetus will respond with a heart rate acceleration. One study found that no instance of fetal acidosis occurred when the baby accelerated in response to the stimulus, and that the test was more likely to provoke a response than scalp puncture in non-acidotic babies.12PubMed. Fetal heart rate response to vibratory acoustic stimulation predicts fetal pH in labor However, the evidence is not entirely clean. A separate study examining simple scalp stimulation (without the acoustic component) found that the direction and magnitude of the heart rate response did not reliably distinguish between pH groups.13PubMed. Response of fetal heart rate to scalp stimulation related to fetal acid-base status
Another technology that generated considerable interest was ST-segment analysis of the fetal ECG (marketed under the trade name STAN), which attempts to detect myocardial oxygen deprivation directly from the heart’s electrical signal. Despite a solid physiological rationale, a large randomized trial found that adding ST-segment analysis to standard EFM did not improve perinatal outcomes and did not reduce cesarean rates.14PubMed Central. A Randomized Trial of Intrapartum Fetal ECG ST-Segment Analysis A review of the broader evidence reached the same conclusion: no effect on cesarean rates.15PubMed. Scientific and clinical evidence for the use of fetal ECG ST segment analysis (STAN)
Monitoring Before Labor Begins
Fetal monitoring is not just a labor-and-delivery tool. In pregnancies considered high risk, various forms of surveillance begin weeks before the due date. The nonstress test, which records the baby’s heart rate for 20 to 40 minutes and looks for accelerations associated with movement, is one of the most common antepartum checks. The biophysical profile combines a nonstress test with an ultrasound assessment of fetal movement, breathing movements, muscle tone, and amniotic fluid volume.
Despite being widely used, the biophysical profile has limited trial evidence behind it. A Cochrane review found no significant differences in perinatal deaths or low Apgar scores between high-risk pregnancies managed with the biophysical profile and those managed with other methods.16PubMed Central. Biophysical profile for fetal assessment in high risk pregnancies
Where antepartum surveillance has stronger evidence is in the use of umbilical artery Doppler assessment for pregnancies with suspected fetal growth restriction. By measuring blood flow patterns in the umbilical cord, clinicians can detect increasing resistance in the placental circulation, which signals worsening insufficiency. A summary of randomized studies found that using umbilical artery Doppler in high-risk pregnancies with suspected growth restriction significantly decreased the likelihood of perinatal deaths compared with management without Doppler.17American Journal of Obstetrics and Gynecology. Doppler assessment of the fetus with intrauterine growth restriction Progressive abnormalities in the Doppler signal, from elevated resistance to absent or reversed blood flow at the end of each cardiac cycle, guide decisions about how closely to watch the pregnancy and when to deliver.18Lynchburg Journal of Medical Science. Umbilical Artery Doppler in Fetal Growth Restriction
Why Epidurals and Other Factors Muddy the Tracing
The heart rate tracing does not exist in a vacuum. Several common labor interventions and physiological variables can change the pattern in ways that mimic or mask fetal distress. Epidural analgesia is probably the most important confounder. Different anesthetic agents have different effects: lidocaine-based epidurals can cause fetal tachycardia in some patients and decreased heart rate variability in others, while bupivacaine is sometimes associated with increased variability, though the response is unpredictable from one patient to the next.19PubMed. The effects of epidural anesthesia on electronic fetal heart rate monitoring Some pathologic-looking heart rate changes after epidural placement are strongly linked to drops in maternal blood pressure or uterine overstimulation rather than to a genuine threat to the baby.
A large analysis of fetal heart rate patterns in term labor found that epidural analgesia was the single most important independent cause of fetal tachycardia, and that the baby’s sex, weight, gestational age, and the duration of labor stages also independently affected the tracing.20PubMed. Fetal heart rate patterns in term labor vary with sex, gestational age, epidural analgesia, and fetal weight These effects were additive, meaning a large baby boy at 41 weeks with an epidural running might produce a tracing that looks meaningfully different from a small girl at 38 weeks without one, even if both are perfectly healthy. Clinicians factor these variables in when they can, but the number of confounders helps explain why interpretation agreement is so poor.
The Patient Experience
For the person actually wearing the monitors, the technology is not a neutral presence. Conventional wired CTG involves two transducers strapped around the abdomen with elastic belts, connected by cables to a bedside machine. This setup limits movement, makes it harder to use upright positions or a birth pool, and can feel physically uncomfortable during contractions. In an Australian national survey, 58 percent of women monitored via wired CTG reported that monitoring had a negative impact on their labor.21PubMed Central. Differences in women’s experiences of labour according to type of fetal monitoring: a quantitative analysis of an Australian national survey
A systematic review of how continuous EFM influences labor experiences identified three recurring themes: some women found the monitors reassuring about their baby’s wellbeing, but others felt anxious about the numbers; many felt physically restricted and uncomfortable; and some felt the technology depersonalized their experience, shifting the focus from them to the machine. Wireless devices consistently drew the most positive response, since they allowed greater freedom of movement.22PubMed. How does the use of continuous electronic fetal monitoring influence women’s experiences of labour? A systematic integrative review of the literature from high income countries A randomized trial directly comparing wireless and wired EFM found that women with wireless monitors reported lower perceived pain and higher birth satisfaction.23PubMed Central. The Effect of the Wireless Fetal Monitoring Used During Birth on the Women’s Comfort, Labor Pain, and Birth Satisfaction
Why Hospitals Keep Using It Anyway
Given the mixed evidence, a reasonable question is why continuous EFM remains the default in most hospital births. Part of the answer is structural: intermittent auscultation requires dedicated one-to-one staffing, which many labor wards simply cannot provide. A nurse can glance at multiple tracings on a central monitor station. That staffing reality, more than the trial evidence, often drives the choice.
The other major driver is legal exposure. Providers frequently argue that they must use EFM to protect themselves from malpractice liability, making it a form of defensive medicine.24PubMed. Defensive versus evidence-based medical technology: Liability risk and electronic fetal monitoring in low-risk births The tracing serves as a paper trail, and its absence can be harder to defend in court than a worrisome pattern that was acted upon. Research into this dynamic has suggested that litigation fears stem not just from actual malpractice claims but from a broader culture in which clinicians adopt the role of “fetal champion,” with the monitoring technology reinforcing that identity.25PubMed. Defensive medicine during hospital obstetrical care: a byproduct of the technological age The result is a technology that persists largely because of legal and institutional incentives rather than because the trial data strongly favor it for low-risk births.
Artificial Intelligence and Newer Hardware
Several research groups are working on AI systems that could read CTG tracings more consistently than humans. A review of the field concluded that machine learning and deep learning techniques have shown promising results in classifying fetal health states from cardiotocography data.26Archives of Computational Methods in Engineering. Artificial Intelligence and Machine Learning in Electronic Fetal Monitoring One study reported a stacking classifier model achieving nearly 99 percent accuracy on a benchmark CTG dataset.27Neural Computing and Applications. Early detection of fetal health status based on cardiotocography using artificial intelligence
However, impressive performance on curated datasets has not yet translated into proven clinical superiority. A head-to-head experimental comparison found that experienced human clinicians actually achieved a higher overall discriminative accuracy for fetal asphyxia than the AI models tested. Deep-learning-assisted judgment did improve specificity, meaning it could help reduce false positives, which is exactly the weakness of current EFM practice. But it did not surpass human accuracy on its own.28PubMed Central. Cardiotocography-Based Experimental Comparison of Artificial Intelligence and Human Judgment in Assessing Fetal Asphyxia During Delivery The most realistic near-term role for AI may be as a second opinion that flags patterns clinicians might miss, rather than as a replacement for human interpretation.
On the hardware side, transabdominal fetal ECG technology is emerging as an alternative to conventional Doppler-based external monitors. A prospective study found that transabdominal fetal ECG had average signal loss of about 5 percent versus roughly 16 percent for Doppler, with the gap widening dramatically when the mother moved: Doppler signal loss jumped to about 31 percent during active positions, while the ECG-based system stayed around 7 percent.29PubMed Central. Quality of fetal heart rate monitoring with transabdominal fetal ECG during maternal movement in labor: A prospective study Given how much of the patient experience complaint centers on being forced to lie still, a technology that keeps working while the mother changes position could address both data quality and comfort.
Fetal Monitoring in Low-Resource Settings
Most of the discussion around EFM assumes access to well-staffed hospitals with reliable electricity and equipment budgets. In low- and middle-income countries, the picture is very different. Many facilities lack functioning CTG machines entirely, and even where machines exist, trained staff to interpret the tracings may be scarce. A review focusing on these settings noted that mobile technology could help reduce barriers to perinatal care access, potentially through low-cost Doppler devices paired with smartphone apps that could transmit heart rate data to remote experts.30PubMed Central. A review of fetal cardiac monitoring, with a focus on low- and middle-income countries In these environments, the question is not continuous versus intermittent monitoring but whether any systematic fetal assessment happens at all.
Remote home monitoring is also being explored in higher-resource settings for antepartum surveillance. A scoping review of continuous remote home monitoring solutions for pregnant women found that the technology is feasible, but flagged ongoing challenges with user compliance, data reliability, and the fact that data security concerns have not been adequately addressed.31PubMed. Continuous remote home monitoring solutions for mother and fetus: A scoping review
Informed Consent and the Right to Choose
One aspect of fetal monitoring that receives surprisingly little attention is whether women are meaningfully informed about their options. In many hospitals, continuous EFM is applied as a default rather than presented as one choice among several. Barriers to genuine informed choice about monitoring include time pressure, institutional protocols, and an assumption by staff that monitoring is simply part of standard care rather than something requiring discussion.32PubMed Central. Fetal monitoring: creating a culture of safety with informed choice
From a legal standpoint, a laboring woman retains the capacity for decision-making throughout labor and delivery, except under extremely limited and rare clinical circumstances. Physical pain, emotional stress, and medical interventions associated with childbirth do not remove legal competence, and no treatment can be given to her or her fetus without her consent.33PubMed. Childbirth Is Not a Medical Emergency: Maternal Right to Informed Consent throughout Labor and Delivery In practice, the gap between that legal principle and the way monitoring decisions are often made on labor wards remains wide. For low-risk pregnancies in particular, where the evidence does not clearly favor continuous EFM over intermittent auscultation, presenting both options and their tradeoffs is an ethical obligation that many institutions have yet to routinely fulfill.