• Dr Peter Chew

Why ovulation prediction kit (OPK) fails

She looked dejected. Her menstruation came again. Her hope of attaining motherhood was dashed once more. She had been using ovulation prediction kit (OPK) to time sexual intercourse for the past 8 months with no result.” Why is it so?” she asked.


Y,30, had been married for the past 2 years. She had been actively trying to conceive for the past one year. Her menstrual periods were regular and her husband’s semen analysis was normal. She was advised by her friend to use OPK to help improve her chances of conception.


What is OPK?

OPK is a home test kit used to track ovulation by measuring the levels of Luteinizing hormone (LH) in the urine. LH is a hormone produced by the pituitary gland of the brain and is involved in triggering ovulation, the release of egg from the ovary. Its levels are usually low in the urine but there is a surge 24-48 hours prior to ovulation, the most fertile time for conception. By identifying the LH surge, couples can time sexual intercourse to maximize their chances of getting pregnant.


When to use OPK?

In women with regular monthly menstrual cycles, the LH surge usually occurs between days 12 to 16. The day of the LH surge may vary from cycle to cycle. It should be noted that the surge may not be observed in every cycle. In women with irregular cycles, it may be difficult to determine when to start using the kit. Daily LH testing can be tedious, costly and impractical especially if the cycle length is long.


How to use OPK?

Testing is done in the morning. When the LH surge occurs, a color change will be seen on the test strip. There are many brands available in the market. Each brand may have its own instructions of testing. Many manufacturers advise testing with the first morning urine sample while some may advise the test to be done with the second urine or late morning sample. Instructions by the manufacturer should be followed to attain optimal result. One should also limit the fluid intake before testing as drinking large amount of liquids before testing can dilute the LH concentration in the urine and make detection of the surge difficult.


Why does OPK fail in helping couples achieving pregnancy?

Although OPK, if done correctly, is accurate in detecting the LH surge, it is not full proof that true ovulation would occur a day or two later. In a study of 43 women in which urinary LH was recorded and analyzed daily, it was found that LH surges consist of many variable and unpredictable patterns and ovulation may not actually happen with each pattern.


In some women, a surge may happen without an egg being released, a condition known as Luteinized Unruptured Follicle Syndrome (LUFS). Women with this syndrome have a normal LH surge and menstruation but no ovulation.


In women with polycystic ovarian syndrome (PCOS), there are false small surges in the urinary LH. This could mislead patient to time sexual intercourse wrongly. Similarly, patients with irregular cycles may end up testing the surge too early or too late and missing the ovulation window altogether. In women near the perimenopausal age, urinary LH could also be elevated without ovulation.


Conception

I explained to Y that even if timing of sexual intercourse using OPK is done at the most fertile period, only one out of four or five women will get pregnant during that menstrual cycle. In other words, the natural rate of conception per cycle is 20- 25 %. There are many other factors that can affect the ability to become pregnant.


Further investigations revealed that Y had endometriosis which was treated accordingly. Subsequently, after another 4 cycles using OPKs, Y finally conceived.


“Getting pregnant is not easy!” she exclaimed.

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