Pregnancy test

Pregnancy test
A modern pregnancy test
MeSH	D011258
MedlinePlus	003432

A pregnancy test is a diagnostic tool designed to determine if a woman is pregnant. The mechanism behind these tests revolves around the detection of certain indicators, most notably the hormone human chorionic gonadotropin (hCG). The presence of hCG is a hallmark of early pregnancy, as it is produced by the syncytiotrophoblast cells of the fertilized ova when they embed into the uterus lining, paving the way for placental development.

Mechanism

Upon the fertilization of an ova, the resultant zygote undergoes implantation into the uterine lining. This event triggers the release of hCG, a hormone whose concentration escalates significantly in the initial weeks of pregnancy, peaking approximately by the 10th week.

Types of Pregnancy Tests

Urine Tests

Urine-based pregnancy tests are commonly used due to their convenience and rapid results. Best results are obtained when the test is conducted around four weeks post the last menstrual period (LMP). Morning urine samples are often preferred as hCG concentrations tend to be higher. However, the accuracy can be influenced by fluid intake which might dilute the urine and hence the detectable hCG levels.

Blood Tests

Blood tests, specifically serum hCG tests, offer a more detailed analysis and can determine pregnancy even before a menstrual cycle is missed.

Obstetric Ultrasonography

Apart from biochemical methods, obstetric ultrasonography offers a direct visualization of the embryo or fetus. Introduced in the 1960s, this imaging technique has become a cornerstone in prenatal care.

Modern Pregnancy Tests

Modern-day tests are sensitive to the beta subunit of hCG, present either in blood or urine. Qualitative tests provide a binary outcome (pregnant/not pregnant), whereas quantitative tests measure exact hCG levels. Pregnancy is typically confirmed with hCG levels above 5mIU/mL in clinical settings. At-home tests, based on lateral-flow technology, have varying sensitivity thresholds depending on the brand.

Accuracy and Viability

The precision of pregnancy tests is governed by various factors:

• Timing of Test: Testing around the anticipated date of the menstrual period maximizes accuracy.
• False Positives: While rare, false positives do occur. They indicate hCG presence but might not confirm a viable pregnancy.
• Viability: A positive test confirms pregnancy but doesn't guarantee its viability. Additional assessments, such as ultrasonography, are needed to ascertain the health of the pregnancy.

Historical Perspective

The journey of pregnancy testing began in the early 20th century, marked by the discovery of hCG. The latter half of the century saw advancements with the introduction of ultrasonography and the inception of home-based hCG testing kits in 1968. These innovations shifted the dynamics of prenatal care and empowered women to initiate the diagnostic process at home.

See Also

• Early pregnancy factor
• Obstetric ultrasonography
• hCG pregnancy strip tests
• False pregnancy

Pregnancy test Resources
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