How to use ovulation predictor kits

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You',ve probably spent much of your adult life avoiding getting pregnant. Yet now that you’re actively trying for a baby it may be taking a little longer than you',d hoped. Here',s how to pinpoint when you are ovulating.

What is ovulation?

Ovulation is the process that results in the release of one or more eggs from your ovary. Each month, between 15 and 20 eggs mature inside one of your ovaries. The largest is pushed out into the pelvic cavity and swept into the fallopian tube.

Your egg only survives for between 12 hours and 24 hours if it is not fertilised. There',s only a small window each month during which you can conceive, typically no longer than about six days. This time leading up to ovulation is when you are most fertile (your fertile window).

It',s possible for sperm to survive inside you for up to about seven days (NCCWCH 2013:68). But the healthiest sperm, with the best ability to swim in a straight line (motility), result from your partner ejaculating every three days to four days (NCCWCH 2013:68) ideally, given that you',re trying for a baby, when you are having sex!

Most conceptions result from having sex in the two days leading up to ovulation (NCCWCH 2013:68) so to increase your chance of pregnancy, you need to ensure that you have sex at this time. An easy way to do this, is to try to have sex a couple of times a week throughout your cycle.

Can ovulation kits help?

Ovulation predictor kits (OPKs) can help you to identify your fertile window. But there is no evidence that using them will improve your chances of getting pregnant naturally (NCCWCH 2013:68). Regular sex throughout your cycle is the best way to maximise your chances of conception (NCCWCH 2013:68).

However, you may prefer to schedule sex for your fertile period if:

• You or your partner works away from home a lot, which makes regular sex difficult.
• You and your partner have hectic schedules and already have children. Sex may not be a priority, and having sex every two to three days may feel like just another chore .
• You have an irregular cycle. which makes it more difficult to conceive.

There are a few ways to determine your fertile window. You could record your menstrual cycle. chart the monthly cycles of your basal body temperature. or study changes in your cervical mucus. Or you could try all three.

However, it can be tricky to pinpoint ovulation using these methods, especially if your menstrual cycles are irregular. This is where ovulation predictor kits (OPKs) can help.

An OPK is a quick, easy and accurate way to predict ovulation in advance (Eichner and Timpe 2004). It allows you to pinpoint your fertile window from the very first month. Kits are available online, and at most chemists and supermarkets. You can usually find them in the same section as pregnancy tests.

How ovulation kits work?

Urine-based OPKs test your urine for an increase (surge) in luteinising hormone (LH). This happens one day to two days before ovulation.

A small amount of LH is always present in your blood and urine. But in the days before ovulation, the amount increases by about two to five times. The 12 hours to 36 hours between the beginning of the LH surge and the moment when your egg is released is the most fertile part of your cycle. This is when you are most likely to conceive.

Salivary ferning kits allow you to test your saliva with a pocket-sized portable microscope. As your oestrogen levels rise, the salt content of your saliva increases. When the salt dries, it crystallises into a fern-like pattern.

Ferning is more likely to occur in the few days leading up to ovulation, so checking for this helps to identify your fertile window.

How do I use an ovulation kit?

Depending on the brand of urine-based OPK, you',ll either collect your wee in a cup or hold a stick under you as you wee. Coloured bands will appear on the test card or stick to indicate whether or not the LH surge is occurring. Digital OPKs use symbols, such as a smiley face, to tell you when you are on your most fertile days.

Instructions may vary slightly depending on which kit you use, but in general you should try to collect your urine between 10am and 8pm. The optimum time is supposed to fall between 2pm and 2.30pm.

Try to collect your urine at about the same time every day, though this is not absolutely necessary. Don',t test your urine as soon as you wake up, because you may miss the first day of your LH surge. Try to reduce the amount of liquids you drink for about two hours before you do the test. Too much liquid will dilute your urine, which could make it more difficult to detect the surge.

Read the results within 10 minutes for the best results. A positive result will not disappear, but some negative results may later display a faint second colour band. So throw the test card away once you',ve read the result. Urine-based OPKs generally provide five to nine days', worth of tests.

Using a salivary ferning OPK is perhaps easier, as all you have to do is place some of your saliva on a slide by using your finger or licking it. Do this first thing in the morning, before you',ve had anything to eat or drink. Make sure you don',t put too much on and that it is free of any air bubbles.

You then wait for the saliva to dry and then use the microscope to see whether there is any ferning or not. Compare your slide with examples in the instructions to see whether you',re in your fertile window.

With either type of OPK, it helps to work out when your fertile period is likely to start. It',s usually the length of your usual cycle minus 17 days. So, if you have a 28-day cycle, start testing on day 11 and carry on for six days. Use our ovulation calculator to help you work out when your fertile window is likely to be.

What else should I know?

Paracetamol and other common drugs don',t affect the tests. However drugs containing human chorionic gonadotrophin (hCG) or LH can affect the test results, and clomid can affect salivary ferning test results (Pattanasuttinont et al 2007, Berardono et al 1993).

Urine-based LH tests are about 99 per cent accurate and are probably the best method of ovulation prediction available for home use (Eichner and Timpe 2004). But they',re not foolproof.

The kits can measure LH, but since LH can surge with or without the release of an egg, they can',t indicate whether you have definitely ovulated after a positive response. What',s more, false LH surges can take place before the real one. Most importantly, you should never use these kits as a contraceptive, since you can still become pregnant for about 24 hours after ovulation.

Salivary ferning tests aren',t as accurate as LH tests (Eichner and Timpe 2004). Ferning may happen at other times in your menstrual cycle, particularly if you are taking clomid (Pattanasuttinont et al 2007, Berardono et al 1993). It may also be hard to judge if ferning has happened or not (Guida et al 1999). If you have poor eyesight, salivary ferning kits may not be the best method for you.

How much will it cost?

Standard urine-based OPKs cost between £10 and £15 per cycle. Most brands offer the same level of reliability, so pick the one that offers you the most tests for the least amount of money.

All kits come with a list of frequently asked questions about performing the test. Once you use the test and detect your surge you can stop testing for that cycle. You can then save any unused tests for the following month (unless you conceive, of course!).

Salivary ferning OPKs can be better value. After the initial outlay of about £20 to £40 for the microscope, you should be able to use it again and again. However, if it takes you a long time to conceive, depending on the brand, you may have to replace it with a new kit after about two years.

Talk to others who are hoping to get pregnant by joining our Actively trying group.

Last reviewed: April 2013

References

Berardono B, Melani D, Ranaldi F, et al. 1993. Is the salivary ",ferning", a reliable index of the fertile period? Acta Eur Fertil. 24(2): 61-5

Eichner SF, Timpe EM. 2004. Urinary-based ovulation and pregnancy: point-of-care testing. Ann Pharmacother. 38(2): 325-31

Fehring RJ, Schneider M, Raviele K. 2006. Variability in the phases of the menstrual cycle. J Obstet Gynecol Neonatal Nurs. 35(3): 376-84

Germano E, Jennings V. 2006. New approaches to fertility awareness-based methods: incorporating the Standard Days and Two Day Methods into practice. J Midwifery Women',s Health. 51(6): 471-77

Guida M, Tommaselli GA, Palomba M, et al. 1999. Efficacy of methods for determining ovulation in a natural family planning program. Fertil Steril. 72(5): 900-4

Lynch CD, Jackson LW, Buck Louis GM. 2006. Estimation of the day-specific probabilities of conception: current state of the knowledge and the relevance for epidemiological research. Paediatric Perinatal Epidemiol. 20(suppl): 3-12

NCCWCH. 2013. Fertility: assessment and treatment for people with fertility problems. National Collaborating Centre for Women',s and Children',s Health, Clinical Guideline. London: RCOG Press. www.rcog.org.uk [pdf file, accessed April 2013]

Pattanasuttinont S, Sereepapong W, Suwajanakorn S. 2007. The salivary ferning test and ovulation in clomiphene citrate-stimulated cycles. J Med Assoc Thai. 90(5): 876-83

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