BOSTON, MA — A genetic contraceptive that could interfere with the consistency of women’s eggs during ovulation each month and which is also designed to have none of the side effects of traditional hormone-based pills is being developed by scientists. The new approach, the researchers say, should make it impossible for a woman using the genetic contraceptive to get pregnant. Because a genetic contraceptive will not flood the body with sex hormones it will avoid many of the side effects caused by conventional birth control pills.

Current oral contraceptives, which are based on the steroids progesterone and estrogen, have been linked to an increased risk of blood clots and may also affect mood and sex drive and cause weight gain.

The new contraceptive relies on a technique called RNA interference, which uses small fragments of genetic material to block the activity of genes in the body. The process is so powerful it was lauded as a revolution in medical science last year, when two American scientists, Andrew Fire and Craig Mello, won the Nobel prize for their work on it.

Zev Williams and his team at Brigham and Women’s Hospital in Boston, part of Harvard Medical School, use RNA interference to block a gene called ZP3 that only appears in eggs when they are being ovulated. Normally, the gene produces a protein that coats the outside of the egg, the zona pellucida, and is vital for sperm to latch on to, to achieve fertilization.

“If you could block this in women, you could prevent pregnancy from occurring,” Williams said, to the press. “For women who use the pill just as a contraceptive, a non-hormonal approach would be wonderful. You could get all the benefits without the nausea, the headaches, the mood alterations, and the raised risk of thrombosis, stroke and heart attacks.”

The scientists hope to begin full tests on animals within five years, and if it works, the genetic contraceptive — most likely in the form of a suppository or skin patch — could be available to the world’s women within 10 years.