Dec. 8, 2004 -- Male fertility may be affected by perching laptop computers on the lap, according to a new study.

Balancing laptop computers on the lap raises the scrotum's temperature, say researchers including Yefim Sheynkin, MD, FACS, of the urology department at the State University of New York at Stony Brook.

About 15%-20% of couples that want to get pregnant aren't able to conceive. Many of those cases trace back to issues relating to the male. Gradually declining sperm production has been noted in recent decades, say the researchers.

Elevated scrotal temperatures have been linked to male infertility. Many factors can raise scrotal temperature, including hot baths, saunas, and tight jockey shorts.

Laptop computers may also belong on that list, say Sheynkin's team. They studied 29 healthy young men ages 21 to 35 for two, one-hour sessions in a climate-controlled room.

Participants were all similarly dressed in casual clothes. After having their body temperature taken and standing in the room for 15 minutes to adjust to the room's temperature, they sat down and were given working or nonworking laptop computers.

The researchers used two brands of Pentium 4 laptop computers. The brands aren't identified in the study, which appears in the European journal Human Reproduction.

The men balanced the computers on their laps. The researchers then removed the nonworking computers, instructing the men to hold the position for the rest of the session. Participants with working laptop computers kept the computers in place throughout the session.

The men's scrotal temperature was recorded every three minutes. The temperature on the bottom of the working computers was also monitored.

Scrotal temperature rose with the working and nonworking computers. However, the working laptops prompted a greater increase in scrotal temperature -- around a 5 degrees Fahrenheit increase (or about 2.7 degrees Celsius).

Participants without working laptops had a scrotal temperature increase of about 3 to 4 degrees Fahrenheit (2.1 degrees Celsius).

Technology doesn't deserve all the blame. The position required to balance a laptop computer in the lap -- with thighs close together to balance the computers -- also increases scrotal temperature. Still, the heat generated by the laptops adds to the problem.