The clearblue fertility monitor is a palm sized device that uses an electronic algorithm to help women identify typically up to five days of high fertility before they reach peak fertility, thereby maximising the chance of a successful conception. Use of this product also removes any subjective interpretation of line intensity that can occur in a visual reading. You must start using the fertility monitor by the 5th day of your cycle. Proven to increase the chances of getting pregnant naturally by 89 tracks two key fertility hormones designed to detect all your fertile days monitor and refill sticks are sold separately pregancy can be validated by ultrasound 99 accurate at detecting the lh surge and over 99 accurate at detecting pregnancy from the day your period is due