These probes/sensors work with the FD300 and FD320 Fetal Dopplers. We have 2Mhz probes and 3Mhz probes. The 2Mhz/3Mhz probes can be used to hear your baby's heart beat. If you want to hear your baby's sound/movement, please choose the either 2Mhz or 3Mhz probe.
A 3MHz probe is recommended to detect a heart rate in early pregnancy (8-10 weeks gestation). A 3 MHz has also been proven to work well throughout the pregnancy.
A 2MHz probe is recommended for pregnant women who are overweight.