Ovulation prediction kits (OPKs) can help calculate when you are most fertile, and time intercourse to maximise your chances. Here is a round up of how they work and why to use them, and also what you should be aware of!
How do ovulation prediction kits work?
There are only a few days per cycle when a woman is fertile and can conceive.
The ‘fertile window’ usually spans 6 days, starting approximately 5 days prior to ovulation and ending on the day of ovulation itself.
The 6-day fertile period is affected by:
- The lifespan of the egg, which is up to 24 hours after ovulation
- The lifespan of sperm which is more variable but can last around 3-5 days depending on the environment such as the cervical mucus.
The two most fertile days of this 6-day fertile window are known as peak fertility days. These peak fertility days are the day prior to ovulation and the day on which ovulation takes place.
There is always a small amount of a hormone called the luteinising hormone (LH) in urine but it increases dramatically once a month around the time you ovulate. This increase is known as the LH surge.
A surge in LH level occurs 24-36 hours prior to ovulation, and this can be used to predict when ovulation will occur.
Ovulation test kits pinpoint ovulation by measuring when this happens
When the test turns positive, the LH is surging and this suggests ovulation is imminent. By identifying the ‘fertile window’ you can make sure you have sex (and therefore sperm in your system to meet the egg).
Some tests also measure another hormone called estrone-3-glucuronide (E3G). This is produced when estrogen breaks down in your body and accumulates in urine around the time you are ovulating.
How to use them?
Start testing from the 10th to 11th day of a new cycle (day 1 is defined as the first day of menstrual bleeding), or 4 days before the estimated ovulation day
Test urinary LH once or twice daily.
The test will be read as positive or negative.
A positive result predicts ovulation within 36 hrs
Are there downsides?
The LH surge, which OPKs detect may NOT be followed by true ovulation.
NICE Fertility guideline and a 2015 Cochrane review state using OPKs to predict ovulation to time intercourse doesn’t improve the chance of natural conception.
False positives may actually indicate pregnancy – OPKs test surges of LH in your urine. A pregnancy test detects the presence of human chorionic gonadotropin (hCG). Both of these (LH and hCG) are known as glycoproteins, and share similar protein components.
They’re so similar, that ovulation tests are sometimes unable to distinguish between them. If you have enough LH or hCG in your urine, your ovulation predictor kit may read either as a positive.
Do they work with PCOS?
PCOS causes hormonal changes which mean the surge in LH may not result in ovulation.
Talk to your GP if you have been testing your hormone levels for a few months and the results seem odd or are consistently not showing ovulation.
Conclusion
OPKs can be a useful tool to identify the fertile window and prompt further investigation if there is a suspicion a woman is not ovulating.
However, it should not be relied upon as a true marker of ovulation. If a couple find it difficult to have sexual intercourse every 2 to 3 days, the prediction of ovulation using LH kits can be useful. This post contains more information about the tests that may be used to confirm if you are ovulating.