> ## Documentation Index > Fetch the complete documentation index at: https://docs.sonohealth.com/llms.txt > Use this file to discover all available pages before exploring further. # 2.5 MHz vs 3 MHz Fetal Doppler — Which Probe Frequency Is Better? > 2.5 MHz vs 3 MHz fetal doppler: which probe frequency is better for home use? Comparison of depth, sensitivity, detection range, and who each is best for. **For most home users, 2.5 MHz and 3 MHz both work well — but 2.5 MHz has a practical advantage for users with higher BMI or for earlier detection.** The SonoHealth HeartBeats™ uses a 2.5 MHz probe. Here's what the difference actually means. ## At a Glance | | 2.5 MHz (HeartBeats™) | 3 MHz | | ------------------------------- | --------------------- | --------------- | | **Tissue penetration depth** | Deeper | Shallower | | **Resolution at surface** | Moderate | Slightly higher | | **Best for higher BMI** | ✅ Yes | Less effective | | **Best for lean body type** | ✅ Yes | ✅ Yes | | **Early detection (10–12 wks)** | Slightly better | Slightly less | | **Standard for home dopplers** | ✅ Common | ✅ Common | ## How Ultrasound Frequency Affects Performance In diagnostic ultrasound, there is a fundamental trade-off: **higher frequency = better resolution but less depth penetration. Lower frequency = deeper penetration but slightly less surface resolution.** * **3 MHz** produces shorter wavelengths, which create sharper images at shallow depths but don't travel as far through tissue * **2.5 MHz** produces slightly longer wavelengths, which penetrate deeper into tissue before attenuating For fetal heart detection specifically, the target (fetal heart) is located anywhere from 3–12+ cm deep depending on gestational age, body composition, and baby's position. ## Why 2.5 MHz Is the Better General Choice For home use across a diverse population, 2.5 MHz provides a slight practical advantage: **Higher BMI:** Adipose tissue attenuates ultrasound waves more than other soft tissue. Users with more abdominal depth are more likely to get reliable detection with 2.5 MHz than 3 MHz. **Early pregnancy:** In the 10–14 week window, the uterus and fetus are still low and relatively deep. 2.5 MHz's deeper penetration can help in this window. **Versatility:** 2.5 MHz performs reliably across a wider range of body types and gestational ages. ## When 3 MHz Might Perform Similarly For lean users in the second trimester, 3 MHz and 2.5 MHz produce essentially equivalent results. If baby is large and well-positioned, probe frequency becomes less of a deciding factor. ## What This Means for the HeartBeats™ The SonoHealth HeartBeats™ uses a **2.5 MHz probe** — the same frequency used by handheld clinical dopplers in most medical settings. This was a deliberate choice to maximize reliable detection across the widest range of users. 2.5 MHz · FDA-Cleared · 2-Year Warranty · \$69