fetaldopplerFACTS.org
What's the difference between a 2MHz
and 3MHz fetal doppler probe?

All baby heart monitors designed for fetal heartbeat monitoring is equipped with either a 2 or 3mghz probe. With a 2mghz probe the beam is narrow and direct which helps it penetrate deeper (3-5cm compared to 1-2cm) and find the fetal heartbeat earlier than 3mghz dopplers.

There is a lot of information available stating that the 3mghz fetal doppler probe actually allows the user to find the heartbeat much easier and earlier. We disagree. In our tests and review we found that a 2mghz doppler probe picked up the fetal heart rate at 8 weeks 80% more of the time than a 3mghz probe. Part of the argument for the 3mghz probe enabling easier detection of the heartbeat comes from the belief that because the higher frequency probe has a wider beam the heartbeat is easier to find. When in fact after 12 weeks gestation either probe is easy to find the heartbeat with. This and the fact that a 2mghz probe is much more useful for overweight woman is why we recommend the 2mghz probe and feel it's a better all around probe.

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