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
