Obstetrical Probes SD2 - 2MHz Probe The 2 MHz obstetrical probe is optimized for deep penetration and third trimester pregnancy. SD3 - 3MHz Probe The 3 MHz obstetrical probe is optimized for early fetal heart detection and designed for use during the entire pregnancy (It is the best general purpose obstetrical probe). Vascular Probes SD4 - 4MHz Probe The 4 MHz vascular probe is designed to ease location of blood vessels. The broad, wide-angle beam has internally tilted crystals that are optimized for quickly locating vessels. SD5 - 5MHz Probe The 5 MHz vascular probe is designed to ease location of deeper vessels. The medium width beam and pencil-style shape provides optimum sensitivity and ease of use. SD8 - 8MHz Probe The 8 MHz vascular probe is designed to ease location of surface vessels. The narrow beam and pencil-style shape provides optimum sensitivity and ease of use (It is the best general purpose vascular probe).