No need for condoms, just two doses of 15 minute ultrasound sessions to the testicles could be the future of male birth control, according to new research on rats that demonstrated that currently available ultrasound machinery could be used to kill sperm-growing cells.

Scientists from the University of North Carolina are convinced that if the method is studied further to determine the time span of contraceptive effect and its safety, it could potentially be used on humans.

Dr. James Tsuruta led the research that found that high frequency sound waves can effectively cut sperm counts in rats, and that the equivalent outcome would result in reversible infertility in men. 

“Unlike humans, rats remain fertile even with extremely low sperm counts. However, our non-invasive ultrasound treatment reduced sperm reserves in rats far below levels normally seen in fertile men,” Tsuruta said.

Fertile men are defined to have more than 39 million sperm when they ejaculate, and low sperm concentration is defined as less than 15 million sperm per milliliter, according to the World Health Organization.  

Researchers were able to demonstrate the contraceptive effect by placing rat testes in a cup of saline, and using rotating high frequency ultrasound at 3 MHz on the testes for two 13-minute sessions at two days apart, the temperature of the rat testicles rose to 37 degrees centigrade which reduced sperm to a Sperm Count Index of zero.

The method worked because testes need to be cooler than the rest of the body in order to produce sperm, and therapeutic ultrasound, which has also been used to heat joints to increase circulation, warms the testes in a way that depleted developing germ cells from the testes and led to the decrease in the size of sperm reserves.

The idea of ultrasound being used as a male contraceptive was first proposed in 1975 when Dr. Mostafa Fahim of the University of Missouri demonstrated the effectiveness of ultrasound contraception in dogs, cats, rats, monkeys and eight human men, but because the ultrasound devices that were used then have since become outdated, Tsuruta wanted to see if modern ultrasound equipment that is generally used for physical therapy could also be used as a male contraceptive. 

“The non-invasive nature of ultrasound and its efficacy in reducing sperm count make therapeutic ultrasound a promising candidate for a male contraceptive,” the researcher wrote in a statement.

"A permanent or reversible method of contraception based on therapeutic ultrasound treatment could encourage more men to share greater responsibility for family planning," the researchers wrote in the study, published online in the journal Reproductive Biology and Endocrinology on Jan. 29.

Researchers noted that this type of ultrasonic sterilization may also be adapted to induce permanent infertility in a noninvasive way to sterilize household pets.