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Clearblue offers a range of pregnancy tests, all of which detect the clinically proven urinary pregnancy marker – human chorionic gonadotrophin (hCG) to provide accurate and trusted results.

How hCG is used to detect pregnancy

HCG is produced in the earliest stages of pregnancy. During early pregnancy it plays a role in survival of the corpus luteum1 and has a significant role in the implantation of the blastocyst and protection of the embryo against immune attack at the foetal/maternal boundary. The hormone is initially produced by the embryo and therefore acts as a marker for its presence.2

HCG levels rise rapidly and predictably in the earliest days of pregnancy3 and it can be detected in urine 9-10 days following estimated day of conception when using the most sensitive laboratory assays4. The levels of hCG in early pregnancy have also been found to be highly similar between women4. This makes hCG an ideal urinary marker for quickly and accurately assessing whether a woman is pregnant or not.

Clearblue Pregnancy Tests can be used up to 4 days before the period is due.

Published literature shows that hCG levels reach at least 50 milli-International Units per milliliter (mIU/ml) on the day a pregnant woman's period is due5-7. If a Clearblue Pregnancy Test is used from the day the period is due, it is more than 99% accurate in detecting the presence of hCG8. Whilst Clearblue recommends that women test from the day the period is due, the high sensitivity of the Clearblue Pregnancy Test also means that pregnancy can be detected up to 4 days before the period is due for women who wish to test early. The graph below shows a typical rise in urinary hCG from the first detection of pregnancy.

An example of the daily hCG rise in early pregnancy urine samples
Day 0 indicates the day the period was due.

Not all pregnant women who test before the day of their expected period will obtain a 'Pregnant' result. This is because urinary hCG levels may not yet be above the threshold for the test.

Clearblue Pregnancy Tests are rigorously tested using early pregnancy urine samples from women whose luteinising hormone (LH) surge day is known and from which the day the period is due can be reliably estimated7. Using these samples it is possible to assess the proportion of pregnant women expected to have sufficient hCG in their urine sample to generate a 'Pregnant' result, on each specific post-conception day. If women choose to test early, the likelihood of detecting pregnancy before the day the period is due is clearly displayed on the product packaging. Any woman who tests and gets a 'Not Pregnant' result, but still suspects pregnancy, should test again the day the period is due if testing was done early, or 3 days later if the period is overdue.

Clearblue tests are over 99% accurate from the day the period is due

HCG levels can vary a little between women. However, if a Clearblue Pregnancy Test is used from the day the period is due, it is more than 99% accurate in detecting the presence of hCG8. Circulating levels of hCG can increase with age in women, particularly around the menopause, and it has been proposed that this may lead to false positive results with pregnancy testing kits, particularly for perimenopausal women9. Clearblue Digital Pregnancy test with Conception Indicator has been tested using urine panels from peri and postmenopausal cohorts. Using different lots, the pregnancy test gave a false positive rate of 0-0.5%. All positive results were for women who were over 50 years of age.10 At Clearblue we believe that consumers need a result they can be confident in and act on, and therefore we provide products that deliver over 99% accuracy from the day the period is due. Not all pregnancy tests are over 99% accurate from the day the period is due.

How hCG is used to estimate the time since conception

Conception time can be estimated if the LH surge day is known. Studies have shown that the egg survives for only around 0.7 of a day11, and the fertile period ends on the day of ovulation12. LH surge is well validated as a marker of impeding ovulation13, 14, a large multicentred study demonstrated that conception was most likely on the day following the LH surge15. Since conception occurs shortly after ovulation, LH surge can be used to identify the day of conception. Following implantation, hCG levels rise exponentially and predictably in blood and urine so hCG has been used to estimate gestational age16, 17. Rigorous trials have shown that there is a consistent pattern to urinary hCG levels in the first few weeks following conception18 such that thresholds for urinary hCG can be assigned in order to determine time since conception in categories: 1-2, 2-3 and > 3 weeks since conception. These thresholds are employed by the Clearblue Digital Pregnancy Test with Conception Indicator, so that the test provides not only a 'Pregnant'/'Not Pregnant' result, but also an estimate of the time since conception. Furthermore, pregnancy duration estimates using the Conception Indicator result are 98% in agreement with standard of care ultrasound results19.

Digital displays provide more accurate readings

It has been shown that one in four women can misread traditional line pregnancy test results20. The Clearblue Digital Pregnancy Test with Conception indicator contains an optical reader which provides clear digital results and eliminates the human error that can occur when reading traditional line tests20.

The fully integrated Clearblue Digital Pregnancy Test with Conception indicator provides women several important benefits:

Visual signs give consumers confidence

An innovative pregnancy test, designed using customer insights to be the easiest pregnancy test to use.

Over 25 years of consumer research has given Clearblue an exceptional understanding of our consumers’ needs, allowing us to develop the next step in visual home pregnancy tests. Not only is the Clearblue PLUS Pregnancy Test as accurate as a doctor’s urine test23, but it is also designed to be the easiest home pregnancy test to use.

By incorporating a series of innovative design features, the Clearblue PLUS Pregnancy Test combines accuracy with ease of use to offer women a pregnancy test they can trust with confidence:

1 Baird DD, Weinberg CR, McConnaughey DR, Wilcox AJ. Rescue of the corpus luteum in human pregnancy. Biol Reprod 2003 Feb;68(2):448–56.
2 Perrier d'Hauterive S, Berndt S, Tsampalas M, Charlet-Renard C, Dubois M, Bourgain C, et al. Dialogue between blastocyst hCG and endometrial LH/hCG receptor: which role in implantation? Gynecol Obstet Invest 2007;64(3):156–60.
3 Nepomnaschy PA, Weinberg CR, Wilcox AJ, Baird DD. Urinary hCG patterns during the week following implantation. Hum Reprod 2008 Feb;23(2):271–7.
4 Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med 1999 Jun 10;340(23):1796–9.
5 Lenton EA, Neal LM, Sulaiman R. Plasma concentrations of human chorionic gonadotrophin from the time of implantation until the second week of pregnancy. Fertil Steril 1982 Jun;37(6):773–8.
6 Chard T. Pregnancy tests: a review. Hum Reprod 1992 May;7(5):701–10.
7 Johnson, SR., Miro, F, Barrett, S. & Ellis, JE . Levels of urinary human chorionic gonadotrophin (hCG) following conception and variability of menstrual cycle length in a cohort of women attempting to conceive. Curr Med Res Opin 2009 25: 741-748).
8 SPD data on file. Clearblue has been shown to be over 99% accurate from the day of the expected period when compared to a reference method in laboratory studies using urine samples supplied for pregnancy testing.
9 Snyder JA, Haymond S, Parvin CA, Gronowski AM, Grenache DG (2005) Diagnostic considerations in the measurement of human chorionic gonadotropin in aging women. Clin Chem 51, 1830-1835.
10 SPD data on file.
11 Ferreira-Poblete A., The probability of conception on different days of the cycle with respect to ovulation: an overview. Adv Contracept. 1997; 13(2-3):83-95.
12 Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. Effects of the probability of conception, survival of the pregnancy, and sex of the baby. N Engl J Med. 1995; 333(23):1517-21.
13 WHO Temporal relationships between ovulation and defined changes in the concentration of plasma estradiol-17 beta, luteinizing hormone, follicle-stimulating hormone, and progesterone. I. Probit analysis. World Health Organization, Task Force on Methods for the Determination of Fertile Period, Special Programme of Research. Development and Research Training in Human Reproduction. Am J Obstet Gynecol. 1980; 138(4):383-90.
14 Guida M, Tommasselli GA, Palomba S, Pellicano M, Moccia G, Di Carlo C, Nappi C. Efficacy of methods for determining ovulation in a natural family planning program. Fertil Steril. 1999; 72(5):900-4.
15 Gray RH, Simpson JL, Kambic RT, Queenan JT, Mena P, Perez A, Barbato M. Timing of conception and the risk of spontaneous abortion among pregnancies occurring during the use of natural family planning. Am J Obstet Gynecol. 1995; 172(5):1567-72.
16 Rule AH, Michlewitz H, Boyle E, Donahoe M. Use of beta-human chorionic gonadotrophin in gestational aging. Ann Clin Lab Sci. 1985; 15(5):428-34.
17 Fritz MA and & Guo SM. Doubling time of human chorionic gonadotrophin (hCG) in early pregnancy: relationship to hCG concentration and gestational age. Fertile Steril. 1987; 47(4):584-9
18 Johnson, SR., Miro, F, Barrett, S. & Ellis, JE . Levels of urinary human chorionic gonadotrophin (hCG) following conception and variability of menstrual cycle length in a cohort of women attempting to conceive. Curr Med Res Opin 2009 25: 741-748)
19 Johnson SR. Home pregnancy test compared to standard-of-care ultrasound dating in the assessment of pregnancy duration. Curr Med Res Opin. 2011 2011; 27(2):393-401.
20 Tomlinson C, Marshall J, Ellis JE. Comparison of accuracy and certainty of results of six home pregnancy tests available over-the-counter. Curr Med Res Opin 2008 Jun;24(6):1645–9.
21 Pike J, Ellis J, Johnson S, Shaw R, Parkinson, Perry P. Accuracy of the new Clearblue Digital Pregnancy test with Conception Indicator. Human Reproduction Suppl., June 2010.
22 SPD data on file. Clearblue Digital Pregnancy Test with Conception Indicator can be used as early as 4 days before the period is due. The amount of pregnancy hormone increases rapidly in early pregnancy. In clinical testing, Clearblue Digital Pregnancy Test with Conception Indicator detected the pregnancy hormone in 55% of women when testing days before their period was due, 86% at 3 days before their period was due, 97% at 2 days before their period was due and 98% at one day before their period was due.
23 When compared to a doctor’s urine test, Clearblue PLUS Pregnancy Test has been shown to be over 99% accurate from the day the period is due when using urine samples supplied for pregnancy testing. Based on a comparison with standard professional 25mIU/ml urine test to detect hCG.
24 When compared to a laboratory reference method, Clearblue PLUS Pregnancy Test has been shown to be over 99% accurate from the day the period is due when using urine samples supplied for pregnancy testing. Reference method used Reference method used: AutoDELFIA quantitative hCG (Perkin Elmer).
25 Clearblue recommends that women test on the day their period is due. However, the pregnancy hormone increases rapidly in early pregnancy and Clearblue PLUS Pregnancy Test can be used to test 4 days before the period is due, which is 5 days sooner than waiting for the missed period. In clinical testing, Clearblue PLUS Pregnancy Test detected the pregnancy hormone in 56% of women testing 4 days before their period was due, 88% at 3 days before their period was due, 97% at 2 days before their period was due and 98% at day 1 before their period was due.

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