The Surearly Advanced Digital Ovulation Test identifies the fertile window of the menstrual cycle by monitoring two key urinary fertility hormones, estrone-3-glucuronide (E3G; one of the urinary metabolites of estradiol) and luteinizing hormone (LH). By measuring these two hormones, the Clearblue Advanced Digital Ovulation Test is the only ovulation test that accurately detects the timing of a wider fertile period of typically 4 days, 2 more than other ovulation tests.