Washington: A smartphone app that alerts a woman if she is on a high or low risk day for the purpose of planning or avoiding pregnancy would be 96-98 percent effective if used correctly, say researchers. Recognising that each woman's menstrual cycle can vary, the app, called Dot (Dynamic Optimal Timing), allows for menstrual cycles that last as little as 20 days or as long as 40 days. It relies solely on a woman's period start date to provide her with tailored, accurate information about her chance of pregnancy for each day of her cycle -- and it alerts a woman if she is on a high or low risk day for the purpose of planning or avoiding pregnancy. The app was created based on data from several published studies. Dot is one of the few fertility tracking apps -- there are estimated to be about 100 such apps -- that is based on empirical evidence, said one of the researchers Victoria Jennings, director of Institute for Reproductive Health (IRH), Georgetown University Medical Center in Washington, DC. In the European Journal of Family Planning and Reproductive Health Care, the researchers reported the data upon which Dot is based. This includes a detailed fertility analysis of about 1,000 women in six geographical and cultural diverse settings. The World Health Organisation provided most of the data, with additional data from clinical research in the U.S. The researchers believe that Dot, from the beginning, would be 96-98 percent effective in women if used correctly. And as a woman continues to use it, the app increases its individual accuracy. "The more you use Dot -- the more Dot gets to know you," Dot's creator, Cycle Technologies, says on its homepage. Dot has been available for about a year and is increasingly being used globally. Now Jennings and her team at Georgetown's Institute for Reproductive Health will study how women use the app and test the efficacy of Dot as a method to avoid unplanned pregnancy in a real-time situation. "To our knowledge this is the first prospective study on the effectiveness of a 'fertility app,'" Jennings said in a university statement. They are recruiting study volunteers in the US who have downloaded and are using Dot. The participants will be interviewed four times in the yearlong study, and they will answer questions that pop-up in the app that are sent by the researchers.