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
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.Shop HeartBeats™ Fetal Doppler
2.5 MHz · FDA-Cleared · 2-Year Warranty · $79