• Dr Peter Chew

Luteinizing Hormone (LH) and Ovulation Prediction Kits (OPKs)

If you are planning to conceive, the best time to partake in lovemaking would be during ovulation when your ovary releases an egg. Studies have shown that ovulation is controlled by the hormone LH, which is secreted by the pituitary gland, a small pea-sized organ at the base of the brain.

Normally, blood levels of LH are low throughout the menstrual cycle. But 24-36 hours before impending ovulation, LH secretion suddenly rises to very high levels. By identifying the LH surge, you can predict ovulation more accurately and choose the correct time to conceive.

LH surge can be detected in the blood or urine. For convenience and practical reasons, urine estimation of LH using ovulation prediction kits (OPKs) is preferred by patients. These kits are readily available in most pharmacies or may be purchased online.

Most ovulation tests may be done at any time of the day. Some manufacturers suggest using the test with the first morning urine while others suggest doing the test around noon time or in the evening. For better accuracy and consistency, the test should be done about the same time each day. As the urinary levels of the LH fluctuate with fluid intake, it is best to hold the urine for 4 hours before testing,

A positive result indicates the LH surge which signals the “fertile window” for conception in the next 24-48 hours. As the surge usually lasts less than 24 hours, it is important to do the urine tests in sequence around ovulation in order to detect this crucial period.

As most OPKs are quite expensive, it is not necessary to do the test daily or multiple times a day until you get the positive result. You can use your cycle length to gauge approximately the likely period of ovulation and figure out when to start testing. In this way, you can reduce the cost of testing.

In some women with irregular periods, it may be difficult to know when to start doing the tests. In this situation, it is best to consult your gynaecologist or look for other fertility signs such as assessment of cervical mucus before you begin testing.

OPKs only measure the LH surge. It does not confirm that you have actually ovulated. Occasionally, an egg fails to emerge from its follicle after the LH surge, a condition known as luteinized unruptured follicle syndrome.

OPKs also do not work when certain fertility drugs such as FSH or hCG are present in the urine. They are also not reliable in perimenopause and in women with polycystic ovary syndrome (PCOS) when the LH levels are persistently high.

Although in most cases, OPKs provide an accurate forecast of your LH surge and subsequent ovulation, they are most effective when used together with other methods. Combine OPK testing with cervical mucus detection and basal body temperature, and your chances of becoming pregnant will be greatly enhanced.

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