When pregnancy is suspected, go to the pharmacy and buy a test: a now common, almost natural gesture.

With this article, I intend to explain how current over-the-counter pregnancy tests work, their history, and their proper use.

THE FIRST PREGNANCY TESTS

The first biological test for the diagnosis of pregnancy (the Aschheim-Zondek test) was developed in 1927 and consisted of injecting the urine of women who suspected pregnancy into immature mice or rabbits;

Then the ovaries of the animals were examined and if they showed follicular maturation and luteinization, the test was positive.

In 1959, the first immunoassay for pregnancy (Wide-Gemzell test) was developed using rabbit antibodies against the hormone hCG;

In the 1970s, with the advent of monoclonal antibodies and the development of enzyme markers, more sensitive and accurate hCG tests were developed.

The first over-the-counter pregnancy test-launched in 1976 by the Warner-Chilcott company lasted two hours and consisted of a test tube and a tube holder equipped with a special mirror that allowed the results to be read from below.

PROOF OF PREGNANCY TODAY

Pregnancy tests introduced in 1976 are the most widely used diagnostic tests today and determine whether conception has occurred.

They use antibodies to detect hCG: human chorionic gonadotropin, the pregnancy hormone detectable in urine (including blood) 9 days after fertilization:

If a woman is pregnant, her urine will contain hCG whose levels rise at a rate of about 50% per day.

There are many pregnancy tests on the market, the most advanced of which provide reliable results already in the first weeks of pregnancy.

HUMAN CHORIONIC GONADOTROPINE

Human Chorionic Gonadotropin (hCG) is a hormone produced by the trophoblastic cells of the placenta which, after implantation of the embryo, develops and produces increasing amounts of hCG (which is used as a marker to create pregnancy tests).

Human hCG is a glycoprotein consisting of two subunits: one α and one β;

Multiple forms of hCG are detected in the urine and WHO international standards indicate the most important forms (free β subunit and free β subunit affected) to use antibodies directed against the β subunits of hCG as a test method to be used in evidence.

HOW DO THEY WORK

Pregnancy tests today are more complex and sensitive, as well as faster and easier to use than those of the past.

They consist of an immunoassay that uses monoclonal or polyclonal antibodies to bind to hCG and produce a reaction that gives a color change.

For the marker lines, a buffer is used containing mobile antibodies specific for hCG linked to chromophores (dyes) that move by capillarity following the urine with which they come into contact:

T-strip (or “test strip”) containing stable hCG specific antibodies;

A C-strip (or “control strip”) contains antibodies specific to a part of the T-strip antibody that travels with urine.

During C-Strip staining, antibodies-hCG carried in the urine by capillaries also crossed the T-band:

If it is also stained, it means that the hormone is in the urine, and checking the color of both strips confirms pregnancy;

When the T-Strip is only colored, pregnancy is not present;

When the T-bar is not colored, it means that the urine did not come through the capillaries and therefore it is necessary to repeat the test.

Pregnancy is confirmed by the appearance of prominent lines (single line / double streak);

In the case of the most recent digital test, the reaction is read by an optical sensor which displays the result as “pregnant” or “not pregnant”.

The most advanced version of the pregnancy test, especially the Clearblue digital test, can determine the level of hCG in urine and provide women with an estimate of the length of pregnancy (in weeks).

Accuracy of pregnancy tests

Pregnancy tests claimed to be 99% more accurate when used from the day of the scheduled period, are based on tests reproduced under laboratory conditions rather than real conditions.

In real life, the accuracy of over-the-counter pregnancy tests may be lower, in fact, some studies have shown that the sensitivity of the tests is reduced when people do it at home.

When a specific test is used correctly, there are a few cases where the result is inaccurate.

The most common causes of inaccurate results occur:

When testing before there is a sufficient amount of hCG in the urine for a positive result;

For inaccurate estimates of the onset of a new menstrual cycle by women who take pregnancy tests at inappropriate times (false negatives);

When high concentrations of hCG occur in the form in the later stages of pregnancy (another type of pseudo-negative).

The reliability of pregnancy test results depends not only on the biochemical performance of the test system but also on factors such as test handling, testing procedures, and the easy-to-understand instruction leaflet.

According to some studies, one in four women misinterprets both online tests and product instructions, which is why they do not read test results correctly;

Fortunately, the digital display of results reduces the percentage of interpretation errors as the cause of incorrect results.

Practical advice

To properly perform the test, you must first check the expiration date and strictly follow the instructions on the package.

Even if the test is performed correctly, it can be repeated after a few days;

Some formats have two chopsticks, in order to confirm the result after the first test (they also save money from an economic point of view.

Pregnancy and late period are sensitive issues that can “scare” women;

My advice is to always count on health professionals, doctors, and pharmacists who know, in addition to reassuring you, how to provide precise health advice.

Always consult your doctor when:

You have symptoms early in pregnancy such as nausea, vomiting, breast tenderness, mood, and appetite changes, even if the test result is negative;

The result is not clear and the timing is clear;

A positive result for confirmation of pregnancy with a blood test (plasma test).

Sources

“Hope Bands: The Accuracy of Home Pregnancy Tests and New Developments” – C. Gnuth, S. Johnson-Green IVF, Griffenbroich, Germany; Department of Obstetrics and Gynecology, University of Cologne, Cologne, Germany; SPD Development Company Limited, Bedford, UK

“Embryonic Development and Susceptibility to Pregnancy Tests: The Importance of Early Detection of Pregnancy” – Mary Jane Minkin – Yale University School of Medicine, USA.