The Clearblue advanced digital ovulation test is a breakthrough: not only does it detect the rise in luteinizing hormone (LH), it also monitors the level of another key fertility hormone, estrogen, which increases in the days before the LH surge. Because your partner's sperm can survive in your body for up to 5 days, you can actually become pregnant by having intercourse during the days leading up to ovulation. By tracking these 2 key hormones, this test is able to typically identify 4 or more fertile days leading up to, and including, the day of ovulation, at least twice as many as any other ovulation tests.