<P> Dopplers for home or hospital use differ in the following ways: </P> <Ul> <Li> Manufacturer: popular manufacturers are Baby Dopper, Sonoline, Newman Medical, Nicolet (purchased by Natus), Arjo - Huntleigh, and Summit Doppler (now Cooper Surgical). </Li> <Li> Probe Type: waterproof or not . Waterproof probes are used for water births . </Li> <Li> Probe Frequency: 2 - MHz or 3 - MHz probes . Most practitioners can find the heart rate with either probe . A 3 - MHz probe is recommended to detect a heart rate in early pregnancy (8--10 weeks gestation). A 2 - MHz probe is recommended for pregnant women who are overweight . The newer EchoHeart 5 - MHz transvaginal probes aids in the detection of fetal heart tones (FHT) early in pregnancy (6--8 weeks) and for patients who have a retroverted uterus or throughout pregnancy for FHT detection for women who are obese . </Li> <Li> Heart Rate Display: some Dopplers automatically display the heart rate on a built - in LCD; for others the fetal heart rate must be counted and timed by the practitioner . </Li> </Ul> <Li> Manufacturer: popular manufacturers are Baby Dopper, Sonoline, Newman Medical, Nicolet (purchased by Natus), Arjo - Huntleigh, and Summit Doppler (now Cooper Surgical). </Li> <Li> Probe Type: waterproof or not . Waterproof probes are used for water births . </Li>

Fetal heart rate monitor how does it work