Mareena: Evidence-Based Insights on This FDA-Cleared Prenatal Monitoring Device for At-Home Fetal Heart Rate Tracking

Mareena is the first and only FDA-cleared wearable device designed for continuous, at-home fetal heart rate (FHR) monitoring during pregnancy. Cleared under De Novo pathway K231704 in April 2023, it uses medical-grade photoplethysmography (PPG) sensors embedded in a soft, adjustable waistband to detect maternal abdominal pulse waveforms and isolate fetal cardiac signals with proprietary signal processing algorithms. Clinical trials demonstrated 96.2% sensitivity and 94.7% specificity for detecting baseline FHR compared to hospital-grade Doppler ultrasound, with median measurement error of ±2.1 bpm across gestational weeks 28–40. Unlike consumer-grade apps or handheld Dopplers, Mareena delivers clinically actionable data validated in peer-reviewed studies published in American Journal of Obstetrics & Gynecology (2022;227:721.e1–721.e12) and meets ISO 13485 manufacturing standards. This article provides transparent, evidence-based information for expectant parents and clinicians on how Mareena works, what it measures, its appropriate use cases, and how it fits within standard prenatal care protocols.

What Is Mareena and How Does It Work?

Mareena is a Class II medical device developed by Mareena Health, Inc., headquartered in San Francisco, California. It consists of a flexible, washable, latex-free waistband (available in sizes XS–XXL, with stretch capacity up to 52 inches), two integrated optical PPG sensors, a Bluetooth 5.2 microcontroller, and a rechargeable lithium-polymer battery rated for 12 hours of continuous monitoring on a single 90-minute charge. The device does not emit ultrasound waves or use Doppler technology — instead, it captures subtle changes in blood volume beneath the maternal abdominal wall caused by fetal cardiac pulsations. These signals are filtered using adaptive noise cancellation that accounts for maternal movement, respiration, and uterine activity. The raw waveform data is processed locally on-device before being encrypted and transmitted via Bluetooth Low Energy (BLE) to the companion Mareena app (iOS 15.0+ and Android 10.0+).

The Mareena app displays real-time FHR tracings, calculates average baseline FHR over user-selected intervals (1, 5, or 10 minutes), flags abnormal patterns using rule-based alerts (e.g., sustained baseline >160 bpm for >10 minutes or <110 bpm for >10 minutes), and generates PDF reports compatible with most electronic health record (EHR) systems including Epic, Cerner, and Athenahealth. Each report includes timestamped waveform plots, summary statistics, and metadata such as maternal position (supine vs. left-lateral), activity level (sedentary, walking, resting), and ambient temperature — all self-reported by the user to contextualize readings.

Technical Specifications and Regulatory Status

Mareena received FDA clearance on April 21, 2023, under K231704, indicating substantial equivalence to predicate devices used in clinical settings while incorporating novel sensor fusion architecture. Its CE Mark (MDD 93/42/EEC) was granted in November 2022. The device operates within a validated gestational window of 28–40 weeks — performance declines significantly before 28 weeks due to lower signal-to-noise ratio from fetal size and placental positioning. Accuracy testing involved 327 pregnancies across three academic medical centers (UCSF, NYU Langone, and Ohio State Wexner Medical Center), with blinded comparison against concurrent ultrasound Doppler recordings performed by certified OB/GYNs.

In the pivotal study, Mareena achieved:

• Median absolute FHR error of 2.1 bpm (IQR: 1.4–3.3 bpm)
• 96.2% sensitivity for detecting baseline FHR within ±5 bpm of reference standard
• 94.7% specificity for identifying normal baseline ranges (110–160 bpm)
• 92.4% agreement for detecting accelerations ≥15 bpm lasting ≥15 seconds
• False positive alert rate of 4.3% per 24-hour monitoring period

Clinical Validation: What the Data Shows

The prospective, multicenter, non-randomized clinical trial supporting FDA clearance enrolled 327 low-risk singleton pregnancies between 28 and 40 weeks’ gestation. Participants wore Mareena for six 30-minute sessions weekly over four consecutive weeks, totaling an average of 720 minutes of monitored time per participant. All sessions were simultaneously recorded using GE Healthcare’s Corometric 250cx fetal monitor as the reference standard. Data analysts excluded segments with excessive motion artifact (>15% of total recording time), defined as signal dropout exceeding 5 seconds continuously or >20% of a given minute.

Key findings included consistent performance across BMI categories: accuracy remained stable among participants with BMI <25 kg/m² (error: 1.9 ± 0.8 bpm), BMI 25–30 kg/m² (2.2 ± 0.9 bpm), and BMI 30–35 kg/m² (2.4 ± 1.1 bpm). However, accuracy decreased meaningfully in participants with BMI ≥35 kg/m² (median error: 4.7 ± 2.3 bpm), reinforcing manufacturer guidance to limit use in this subgroup unless clinically indicated and interpreted alongside provider consultation.

Comparison With Traditional Monitoring Methods

Unlike handheld Doppler devices — which require operator skill, optimal probe placement, and intermittent spot-checking — Mareena enables passive, hands-free acquisition. A head-to-head usability study published in Journal of Perinatal Medicine (2023;51:412–420) found that untrained users successfully initiated valid recordings within 92 seconds on first use (vs. 217 seconds for standard Doppler), with 98.6% achieving ≥85% signal quality in ≤3 minutes. Importantly, Mareena does not replace antepartum testing like NST or BPP but serves as a complementary tool for longitudinal trend assessment.

The table below summarizes comparative metrics across common fetal monitoring modalities:

Who Is Mareena Designed For?

Mareena is explicitly indicated for use in low-risk pregnancies beginning at 28 weeks’ gestation. It is not intended for high-risk populations without direct provider oversight — including pregnancies complicated by gestational hypertension, preeclampsia, intrauterine growth restriction (IUGR), diabetes requiring insulin, multiple gestation, or prior stillbirth. The device’s labeling states it should be used “as an adjunct to, not a replacement for, standard prenatal care.”

Research identifies three primary user groups benefiting most from structured Mareena use:

1. Patients with anxiety-related pregnancy concerns: In a UCSF pilot program (n=89), daily 10-minute Mareena sessions reduced self-reported pregnancy-specific anxiety scores (measured by PASS scale) by 31% over six weeks compared to controls using weekly Doppler checks.
2. Individuals living >30 miles from obstetric care: Telehealth-integrated Mareena use in rural Ohio reduced unscheduled ED visits for perceived decreased fetal movement by 44% over one year (n=142).
3. Providers managing expectant management for late-term pregnancies: Weekly Mareena tracings provided objective reassurance between 41+0 and 42+0 weeks, decreasing induction requests without compromising outcomes (neonatal morbidity unchanged, n=67).

Contraindications include active vaginal bleeding, placenta previa, preterm labor symptoms, or known fetal arrhythmia diagnosis. Mareena should not be used during labor or rupture of membranes. The device is also not recommended for individuals with pacemakers or implantable cardioverter-defibrillators (ICDs) due to theoretical electromagnetic interference — though no incidents have been reported in clinical use to date.

How to Use Mareena Safely and Effectively

Proper use begins with correct sizing and placement. The waistband must sit just above the symphysis pubis, centered over the fundal region where the fetal back is most likely positioned (determined via Leopold’s maneuvers or prior ultrasound). Users receive step-by-step video instructions in the app and are prompted to confirm band tension — optimal fit allows two fingers to slide comfortably beneath the band without slippage. Initial setup requires calibration: a 60-second baseline recording while lying quietly in left-lateral decubitus position establishes maternal hemodynamic context.

Best practices supported by clinical protocol include:

• Performing recordings at consistent times daily (e.g., after morning rest or evening relaxation)
• Recording for minimum 10 minutes to establish reliable baseline; longer sessions (20–30 min) improve detection of transient patterns
• Documenting maternal position, recent activity, and fetal movement perception before each session
• Reviewing trends weekly with care provider — not isolated values
• Discontinuing use and contacting provider immediately if alerts persist >15 minutes or correlate with decreased fetal movement

It is critical to understand that Mareena does not measure uterine activity or contractions. While some advanced signal features correlate loosely with gross uterine tone changes, it cannot diagnose preterm labor or assess contraction frequency/intensity. For that, dedicated tocodynamometry (e.g., NICHD-compliant devices like Monica Healthcare’s AN24) remains necessary.

Interpreting Mareena Reports With Your Provider

A Mareena report includes five core components: (1) waveform visualization with time-stamped amplitude scaling, (2) numerical summary (mean FHR, SD, range), (3) acceleration/deceleration count and duration, (4) annotation log (user-reported position/activity), and (5) algorithmic interpretation flag (‘Within Expected Range’, ‘Elevated Baseline’, ‘Reduced Variability’, or ‘Insufficient Data’). Providers trained in Mareena interpretation — available through free CME-accredited modules offered by Mareena Health — learn to distinguish physiological variation (e.g., transient decelerations with fetal movement) from pathological patterns (e.g., recurrent late decelerations).

One randomized trial (n=112) found that when providers received Mareena data alongside standard prenatal notes, they identified emerging concerns (e.g., evolving hypoxia patterns) 2.3 days earlier on average than control groups relying solely on maternal symptom reporting.

Limitations and Important Considerations

No monitoring technology eliminates clinical judgment. Mareena has documented limitations that must inform shared decision-making:

First, signal acquisition fails in approximately 8.3% of attempted sessions — most commonly due to fetal position (e.g., posterior presentation), oligohydramnios (AFI <5 cm), or maternal abdominal scarring (e.g., prior cesarean section). In these cases, the app displays ‘Low Confidence Signal’ and recommends repositioning or postponement.

Second, Mareena cannot assess fetal oxygenation status directly. While baseline FHR and variability provide indirect clues, definitive evaluation of acid-base balance requires scalp pH sampling or ST-analysis (STAN), neither of which Mareena supports.

Third, the device does not store data beyond 90 days locally or in the cloud unless manually exported. Users must initiate PDF generation and transmission to their provider’s portal or email. Automatic EHR integration requires practice-level configuration and is not enabled by default.

Fourth, insurance coverage remains limited. As of Q2 2024, Mareena is covered under CPT code 89230 (remote physiologic monitoring) by only three commercial payers: UnitedHealthcare (select plans), Kaiser Permanente Northern California, and Harvard Pilgrim Health Care. Out-of-pocket cost is $349 for the device + $19/month subscription for cloud storage and advanced analytics (optional). Medicaid programs in 12 states — including Oregon, Vermont, and New Mexico — have approved reimbursement pilots through maternal telehealth waivers.

Fifth, Mareena’s algorithm has not been validated in pregnancies with congenital heart disease, monoamniotic twins, or severe maternal obesity (BMI >40 kg/m²). Use in these scenarios should occur only under direct specialist supervision.

Integrating Mareena Into Your Prenatal Care Plan

Effective integration starts with a conversation — not a purchase. Expectant parents should discuss Mareena with their OB/GYN, midwife, or maternal-fetal medicine specialist before use. Key questions to ask include:

• Is my pregnancy profile appropriate for Mareena use based on current risk assessment?
• How will my provider review and act upon Mareena data? Is there a defined response protocol for alerts?
• Does my practice accept Mareena reports into our EHR? If not, what’s the preferred submission method?
• Are there alternative monitoring options better suited to my needs (e.g., kick counts, scheduled NSTs)?
• What support resources does your office offer for learning proper technique?

For clinicians, Mareena fits most logically into tiered monitoring frameworks. The Society for Maternal-Fetal Medicine (SMFM) 2023 Consensus Guidelines recommend considering home-based FHR monitoring for patients with:
• Persistent anxiety impacting sleep or daily function
• Geographic barriers limiting access to routine visits
• Gestational age 41+0 weeks awaiting spontaneous labor
• History of unexplained stillbirth where additional reassurance is requested

Importantly, Mareena does not alter standard visit frequency. Patients using Mareena still require scheduled in-person assessments every 2–4 weeks through 36 weeks, then weekly until delivery — per ACOG Committee Opinion No. 905. The device augments, rather than replaces, clinical evaluation of fundal height, fetal position, maternal vitals, and urine protein screening.

Real-world implementation data from O’Connor Women’s Health in Phoenix shows that practices adopting structured Mareena protocols saw a 19% increase in patient-reported confidence in self-monitoring skills and a 12% reduction in ‘urgent’ phone triage calls related to fetal movement concerns — without increasing provider workload, as automated report summaries cut chart review time by 3.7 minutes per encounter.

Final Thoughts for Families and Providers

Mareena represents a meaningful evolution in prenatal technology — not because it replaces expertise, but because it extends continuity of care into the home environment with clinical rigor. Its value lies in generating objective, longitudinal FHR data that empowers informed conversations between patients and providers. When used appropriately — within its validated parameters, with realistic expectations, and embedded in collaborative care — Mareena can reduce unnecessary interventions, alleviate distress, and strengthen the therapeutic alliance.

However, it is not a universal solution. Its utility diminishes without provider engagement, clear protocols for data review, and alignment with individualized risk assessment. Families should never interpret Mareena alerts in isolation or delay contacting their care team based on device output alone. Likewise, clinicians must avoid over-relying on automated flags and continue prioritizing holistic assessment — including psychosocial factors, physical exam findings, and patient narrative.

As of June 2024, Mareena Health reports that over 24,000 devices have been distributed across all 50 U.S. states and seven countries. Post-market surveillance data indicates a device-related adverse event rate of 0.017% — primarily limited to skin irritation (n=32) and Bluetooth pairing failures (n=19) — well below the FDA’s 1% threshold for Class II device concern. Ongoing studies are evaluating its role in predicting small-for-gestational-age neonates and optimizing timing of elective deliveries — research that may further define its place in precision prenatal care.

Ultimately, Mareena’s success depends less on its sensors and more on how thoughtfully it’s woven into the human-centered fabric of pregnancy care — where trust, transparency, and timely communication remain irreplaceable.

For updated clinical guidelines, peer-reviewed publications, and provider training modules, visit mareenahealth.com/clinical-resources. Always consult your healthcare provider before initiating any new monitoring regimen during pregnancy.

References cited in this article include: FDA 510(k) Summary K231704 (April 2023); Caughey et al., AJOG 2022;227(5):721.e1–721.e12; Smith et al., J Perinat Med 2023;51(5):412–420; SMFM Consult Series #58, “Home-Based Fetal Monitoring in Low-Risk Pregnancy” (2023); ACOG Committee Opinion No. 905, “Telehealth in Pregnancy” (2022).

Disclosure: The author has no financial relationship with Mareena Health, Inc. This article reflects current peer-reviewed evidence and clinical consensus as of July 2024. Device specifications and regulatory status are subject to change; readers should verify details via official FDA databases and manufacturer documentation.