During the first half of your menstrual cycle, the pituitary gland secretes the hormone LH, or luteinizing hormone, to stimulate a growing follicle in your ovary to produce oestrogen. After the amount of oestrogen reaches the appropriate level, the pituitary gland generates a surge of LH. About 24 to 36 hours later, the follicle releases an egg in the process called ovulation. If you are trying to become pregnant, the ability to recognise when this LH surge begins and ends improves your chances of becoming pregnant by helping you time intercourse to coincide closely with your ovulation.
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Things you need
- 10 to 20 ovulation predictor kits
Test daily with ovulation predictor kits (OPKs) starting a few days before you expect to ovulate. If you know approximately when you ovulate, start testing at least three to four days before your normal ovulation date. If you have no idea when you might ovulate, start testing 17 to 18 days before you expect your period to begin. If your cycle length varies, use your shortest cycle in the last six months to determine when to expect your period. Test between noon and 8 p.m. for the most accurate results.
Watch for your OPK to turn positive. You will always see two lines on an OPK because you always have a small amount of LH in your system. However, when you have your LH surge, the second line on the OPK will turn as dark or darker than the control line. Make sure to read the instructions that came with your OPKs to know how to interpret the results. Some brands require a line to be darker than the control and consider a line that is equally dark to be a negative result.
Continue testing with OPKs until your test turns negative again. Usually you will only see one day with a positive OPK, but it is normal to have positive results for two days. Once the test line turns light again, your surge has ended and ovulation should occur within 36 hours.
Tips and warnings
- Some cycles you may only need to use three to five OPKs. But keeping 10 to 20 on hand helps ensure you don't run out before your LH surge ends, especially if you have very irregular cycles.
- If you are taking the fertility drug Clomid, be careful not to start using your OPKs too soon after you finish the medication. Clomid can cause false positives on OPKs. If you see a false positive and then see your OPKs change to negative, you may think your LH surge has ended days before the surge actually begins.
- OPKs can sometimes miss your LH surge. If you happen to test at the wrong times, testing before the surge begins and after it is on the way down again, you might never get a positive OPK. Checking some of your other fertility signs -- such as cervical mucus, basal body temperature and cervix position -- can help you recognise if ovulation has passed and prevent you from spending days using OPKs after your LH surge has already ended.
- If you have Polycystic Ovary Syndrome (PCOS), you may not be able to use OPKs to detect your LH surge. Women with PCOS produce abnormal amounts of certain hormones, including high levels of LH. Since you may have elevated levels of LH all the time, you may test positive on an OPK even when you aren't having an LH surge.
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- First Response: What Exactly Is LH?
- Fertility Plus: Ovulation Predictor Kit Frequently Asked Questions
- FertilityFriend.com: Can I Ovulate Without Ever Seeing a Positive OPK Result?
- What to Expect; Ovulation: Five Ways to Tell if You Are Ovulating; Heidi Murkoff
- Mayo Clinic; Polycystic Ovary Syndrome: Causes; December 2009