Saliva-based fertility tests are "springing up" all over the U.S. market, the Boston Globe reports. The tests, which indicate ovulation when a woman's saliva forms a "ferning" pattern on the test lens, cost between $27 and $120 and can be used over and over. The FDA approved the TCI-OvuLook Ovulation Tester last year and the MaybeMOM Mini Ovulation Microscope in January. Since then, the FDA has issued waivers to other companies applying for approval of saliva-based fertility tests because they are "similar" to the products already approved and they "pose no conceivable danger." According to the Globe, OvulationScope is now available at Kmart and will soon be available at Wal-Mart and Target. Other saliva-based testers -- such as Donna, MaybeMOM, Ovulite and the TCI-OvuLook Ovulation Tester -- can be purchased online or in drugstores. According to the Globe, the saliva-based tests are "seeking to tap into" the growing U.S. market for fertility products; the market for ovulation testers alone is approximately $41 million and is growing 6% to 7% per year, according to Teresa Prego, associate director of marketing for women's health for Waltham, Mass.-based Inverness Medical Innovations. The companies producing the tests hope they will appeal to women who want a cheaper, more convenient option to other fertility testing products, such as urine-testing strips -- which cost $15 to $30 per month -- and "high-tech fertilization monitors," such as Inverness' ClearPlan, which can cost more than $200 (Goldberg, Boston Globe, 3/12). However, according to Gerald Scholl of the North Shore-LIJ Center for Human Reproduction in Manhasset, N.Y., saliva testers have not yet "caught on." Scholl added that although saliva-based tests are less expensive than other fertility tests, they are also less specific. He said that women with irregular periods or high estrogen levels could receive "distort[ed]" results from saliva-based tests. In addition, Prego said that urine-based tests are "more straightforward and don't require [women] to interpret as much" (Herzlich, Long Island Newsday, 3/12).