Ovulation is the release of an egg from ovaries.
The highest possibility for a woman to become pregnant are the few days before and after ovulation.
The female body makes a substance called Luteinizing Hormone (LH) that triggers the release of the egg.
During most of your menstrual cycle, your body manufactures small amounts of LH. But around the middle of your cycle, your body suddenly increases the amount of the LH for a few days. This sudden increase is called the “LH surge”, and it usually causes the female body to ovulate.
Ovulation usually take place within 40 hours after the LH surge begins. You may not have an LH surge or might not ovulate every menstrual cycle. Even if your menstrual bleeding begins on time, that does not necessarily mean that your body has ovulated.
After ovulation, the amount of LH in your body will return to normal level within 2 days. Unless pregnancy occurs, the cycle of increase and decrease of LH will repeat again after your menstrual period ends.
First you must determine your usual cycle length. To do this, count the number of days from the day your last period (menstrual bleeding) started up to the day before you period begins. For example, if your last period started on the 1st day of the month and your next period starts on the 31st, your cycle length is 30 days.
Find your usual menstrual cycle length on the left side of the WHEN TO START CHART. Look across to find the number of days to count ahead from the first day of your period. This will be the day you begin testing.
If your menstrual cycle varies occasionally, use the average of your last 4 cycles when reading the WHEN TO START CHART. If you are unsure about your usual cycle length, use your shortest cycle length from your past 4 cycles when reading the WHEN TO START CHART.
|When to Start Chart|
|If your menstrual cycle length is this many days long||Count ahead this many days from the first day of your period||If your menstrual cycle length is this many days long||Count ahead this many days from the first day of your period|
Example: “My regular menstrual cycle is 28 days and the first day of my last period started on the 2nd of this month. According to the “When to Start Chart”, I should begin testing my urine for an LH surge on the 11th day of my cycle. The 11th day of my cycle this month is the 12th. This means I should begin testing my urine on the 12th of this month.”
|1||2 (Day 1)||3||4||5||6||7|
Revision date: July 6, 2011
Last revised: by Sebastian Scheller, MD, ScD