Testing kits for both ovulation and pregnancy measure levels of substances in your urine, and provide a visual indicator of a negative or positive result, based on concentration in mIU (milli international units). For ovulation, luteinizing hormone (LH) is released in large quantity by the anterior lobe of the pituitary gland, and stimulates maturation of the follicle and release of the ovum. This spike in concentration initiates a flood of anti-LH antibodies that eliminate LH from the body after ovulation, and reduce it to non-ovulatory (“normal”) levels. These antibodies can be measured from 12-48 (usually 36) hours before ovulation, and is very effective in helping to pinpoint with accuracy the time of peak fertility. For pregnancy, test kits measure the level of human chorionic gonadotropin (hCG), which is released after implantation of a fertilized zygote in the uterine lining. The accuracy of test kits, especially pregnancy kits, depends entirely on the concentration of these substances in your urine, which is dependent on the relative timing between the test, and either ovulation or pregnancy.
Ovulation predicting kits (OPKs)
Prediction of ovulation should accompany detailed charting of your monthly cycle, complete with daily measurement of your basal body temperature (BBT) and observations of your cervical mucous (e.g. consistency, colour, presence or absence, feel). You can begin daily testing of your urine about five days after the end of your period, or several days prior to when other bodily indicators (temperature, cervical mucous) indicate you may be ovulating. Since the test measures levels of LH, which spikes before ovulation, the change from a negative to a positive result gives you a window of up to 48 hours during which intercourse is most likely to result in a pregnancy. However, LH testing should not be used as a contraceptive method, since the fertile period can begin several days before the LH spike due to the sperms’ ability to survive in the female reproductive tract as long as 5 days after intercourse.
In order to provide accurate results that can be used effectively, you should test your urine in mid-afternoon (unlike with a pregnancy test), since LH is produced early in the day. Follow the instructions provided with the kit carefully, as they will ensure an accurate result and interpretation.
There are many test kits on the market today. Results may be indicated either digitally, or with a colour-change paper strip. Among these, there are mid-stream tests, which you hold into your stream of urine, and test strips that can be dipped into a cup. (Collect urine only in a clean, sterile container that will be used only for the test). Test results can be interpreted after a 5 minute reaction period. All tests have a control band or line that tells you if the test is working correctly, and can be compared to the “test” line as an indicator of the actual LH concentration. If the test line is lighter than the control line, the result is negative; a positive result is when the test line is as dark or darker than the control.
Pregnancy testing kits
Implantation occurs approximately 6 to 12 days after fertilization. As soon as 48 hours after fertilization, a blood test can detect levels as low as 1 mIU/ml, but these can be expensive and inconvenient. All pregnancy test kits available for home use measure hCG concentrations in the urine, but they can vary greatly, depending on the brand, with respect to the amount of hCG they are able to detect. The lower the level of hCG that a test is able to measure, the earlier you will be able to accurately detect a pregnancy. The earliest kits, which measure concentrations as low as 20 mIU, can allow you to obtain an accurate, positive result several days before the expected start date of your next period. Others, which may only be able to detect levels down to 100 mIU, must be used several days after the expected start date, when you’re late for your period. (A low-concentration test kit can also detect a pregnancy at a later date, but a high-concentration test is unlikely to detect a pregnancy early on).
Like OPKs, pregnancy tests can either be done as a mid-stream urine test or as a paper strip. Either should provide an accurate result if your hCG levels are sufficiently high for the test to detect a pregnancy. However, unlike OPKs, a pregnancy test – particularly for early detection of a pregnancy – should be taken during your first urination in the morning. Levels of hCG will be highest at this time, when they haven’t been diluted by drinking lots of water. If you can’t take the test at this time, or forget to, waiting four to six hours without anything to drink will be sufficient to obtain an accurate test.
Test accuracy
The accuracy of both ovulation predictor and pregnancy test kits is very high (as much as 97-99%) when administered by a medical laboratory; at home, accuracy can fall to as low as 75%, with both false positives and false negatives. False negative pregnancy tests most often occur with tests taken too early, while false negative and false positive OPKs can indicate either improper test use, or reproductive health issues such as polycystic ovarian syndrome, oligomenorrhea (irregular periods), or early-onset menopause. In this case, consultation with your doctor can help you eliminate causes for concern with false or inconsistent OPK results. Most commonly, however, problems result from failure to closely follow the package directions, and are unlikely to be indicative of the test quality itself. Therefore, be sure to thoroughly read enclosed materials, and choose a time to take your test when you can be relaxed and follow the directions closely.
Conclusion
Home testing kits are valuable tools to help you accurately predict ovulation and detect pregnancy at the earliest possible date. When used properly, and especially in conjunction with careful charting and tracking of your monthly cycles, you can eliminate much of the stress and uncertainty associated with trying to conceive, and focus instead on the joys and excitement of this new stage in your life.
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