The timing of the fertile window can be highly unpredictable, even if you have regular cycles. This high variability makes it important to measure your fertility hormones when you are trying for a baby.
The Luteinising Hormone (LH) is an accepted marker for impending ovulation. LH is present in your body at a certain base level and your LH base levels are usually low. LH begins to surge just prior to ovulation. The peak in LH levels triggers ovulation, which occurs approximately 24-48 hours later.
The day of the LH surge and the day after are your two most fertile days in your cycle. If you have unprotected intercourse within your most fertile days you maximise your chances of becoming pregnant. Identifying your LH surge is therefore important to determine your most fertile days.