Using commercially-available ultrasound technology, scientists have successfully reduced sperm count in rats to a level that would cause infertility in men. Researchers managed to reduce motile sperm to 3 million per cauda epididymis (where sperm are stored), which equates to a Sperm Count Index of zero, measured two weeks after treatment. The research could re-open the door to the investigation of ultrasonic techniques as a practical human contraceptive.

Researchers at the University of North Carolina School of Medicine utilized widely available ultrasound equipment used for physical therapy to expose the testes of anesthetized rates to ultrasound at a frequencies of 1 and 3 MHz at varying power densities, temperatures and durations. Ultrasound transducers were applied to the skin via a saline conductor.

Two 15-minute sessions spaced two days apart were found to be most effective, using a frequency of 3 MHz at a power density of 2.2 W/sq cm and a temperature of 37 degrees centigrade (98.6ºF). This permutation of variables resulted in a motile sperm count 1,000 times lower than the application of wet-heat alone - assessed two weeks after treatment.

The research takes its cues from 1970s work led by Mosfata S. Fahim into the effects of ultrasound upon the sperm levels of cats, dogs, monkeys and humans. The bespoke equipment used for the research was not available to the team at UNC.

This research, which received a grant from the Bill & Melinda Gates Foundation, is led by by Dr. James Tsuruta. The current findings were published today in the journal Reproductive Biology and Endocrinology.

It is not yet absolutely clear how long-lasting the effects of treatment are, nor if there are safety implications for repeated use. The end goal is to see if commercially available ultrasound equipment could provide a safe, viable and impermanent means of male contraception.