Pregnancy test Pen and Strip details :

Back Ground :

A pregnancy test attempts to determine whether a woman is pregnant. Markers that indicate pregnancy are found in urine and blood, and pregnancy tests require sampling one of these substances. The first of these markers to be discovered, human chorionic gonadotropin (hCG), While hCG is a reliable marker of pregnancy, it cannot be detected until after implantation.

History :

Records of attempts at pregnancy testing have been found as far back as the ancient Greek and ancient Egyptian cultures. The ancient Egyptians watered bags of wheat and barley with the urine of a possibly pregnant woman. Germination indicated pregnancy. The type of grain that sprouted was taken as an indicator of the fetus's sex. Some suggested that a woman who had missed her period should drink a solution of honey in water at bedtime: resulting abdominal distention and cramps would indicate the presence of a pregnancy.

Modern Tests:

Most chemical tests for pregnancy look for the presence of the beta subunit of hCG or human chorionic gonadotropin in the blood or urine. hCG can be detected in urine or blood after implantation, which occurs six to twelve days after fertilization. Quantitative blood (serum beta) tests can detect hCG levels as low as 1 mIU/mL, while urine test strips have published detection thresholds of 10 mIU/mL to 100 mIU/mL, depending on the brand. Qualitative blood tests generally have a threshold of 25 mIU/mL, and so are less sensitive than some available home pregnancy tests. Most home pregnancy tests are based on lateral-flow technology.

Accuracy :

A systematic review published in 1998 showed that home pregnancy test kits, when used by experienced technicians, are almost as accurate as professional laboratory testing (97.4%). When used by consumers, however, the accuracy fell to 75%. Many users misunderstood or failed to follow the instructions included in the kits. Improper usage may cause both false negatives and false positives.

Timing of test :

The accuracy of a pregnancy test is most closely related to the day of ovulation, not of the act of intercourse or insemination that caused the pregnancy. It is normal for sperm to live up to five days in the fallopian tubes, waiting for ovulation to occur. It could take up to 12 further days for implantation to occur, meaning even the most sensitive pregnancy tests may give false negatives up to 17 days after the act that caused the pregnancy. Because some home pregnancy tests have high hCG detection thresholds (up to 100 mIU/mL), it may take an additional three or four days for hCG to rise to levels detectable by these tests meaning false negatives may occur up to three weeks after the act of intercourse or insemination that causes pregnancy.

False positives :

False positive test results may occur for several reasons. These include: errors of test application, use of drugs containing the assay molecule, and non-pregnant production of the assay molecule.

Spurious evaporation lines may appear on many home pregnancy tests if read after the suggested 3–5 minute window or reaction time, independent of an actual pregnancy. False positives may also appear on tests used past their expiration date.

A woman who has been given an hCG injection as part of infertility treatment will test positive on pregnancy tests that assay hCG, regardless of her actual pregnancy status.

Some diseases of the liver, cancers, and other medical conditions may produce elevated hCG and thus cause a false positive pregnancy test. These include choriocarcinoma and other germ cell tumors, IgA deficiencies, heterophile antibodies, enterocystoplasties, gestational trophoblastic diseases (GTD), and gestational trophoblastic neoplasms (GTN).

Viability :

Pregnancy tests may be used to determine the viability of a pregnancy. Serial quantitative blood tests may be done, usually 3-4 days apart. Below an hCG level of 1,200 mIU/ml the hCG usually doubles every 48–72 hours, though a rise of 50–60% is still considered normal. Between 1,200 and 6,000 mIU/ml serum the hCG usually takes 72–90 hours to double, and above 6,000 mIU/ml, the hCG often takes more than four days to double. Failure to increase normally may indicate an increased risk of miscarriage or a possible ectopic pregnancy.

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