From toad to point-of-care technology - a giant leap for pregnancy management
Pregnancy testing has come a long way in the last 100 years. Prior to the late 1920s confirmation of pregnancy was more of an art than a science and most women relied on nothing more than their own symptoms, such as morning sickness and cessation of periods, to indicate that conception had occurred.
Human chorionic gonadotropin (hCG)
In the 1920s scientists discovered a hormone that was only found in pregnant women (now known to be human chorionic gonadotropin) and which, excreted in urine, promoted ovary development in mice. This became the first scientific pregnancy test, the A-Z test, named after the scientists who developed it (Aschheim and Zondek). The woman's urine would be injected into immature female mice and several days later the mice would be killed and dissected. Development of ovaries would indicate a positive result.
Similar tests were developed using other animals such as rabbits and rats, but they were slow and expensive and all required the death of the animal. In 1939 another bioassay for hCG was developed, using the African clawed toad (Xenopus laevis). Unlike the rodent tests, this didn't require the death of the animal, which could be used again and again. A woman's urine was injected into the dorsal lymph sac of a female toad. If the woman was pregnant, eggs would develop in the toad within 4-12 hours. It was known as the Hogben or Xenopus test.
Modifications of this test used male toads (examining for the production of spermatozoa) and frogs, and were widely used throughout the 1940s and 50s until the development of immunological methods in the 1960s.
The first immunoassay for hCG was the haemagglutination inhibition (HI) test, developed in 1960. Using purified hCG and antibodies directed towards hCG, urine from a pregnant woman would cause the red cells in the HI test to clump together in a distinctive pattern. This method revolutionised pregnancy testing, since animals were no longer required, but it was still relatively insensitive and cross-reacted with certain medications.
Later in the 1960s radioimmunoassays (RIAs) for hCG were developed, measuring levels of radioactive-labelled hCG (attached to hCG antibodies) displaced by ‘cold' hCG in a sample. However, these RIAs were unable to differentiate between hCG and luteinising hormone (LH), the hormone that stimulates ovulation, and so lacked specificity. It wasn't until the 1970s that a RIA specific for hCG became available (directed towards the ß-subunit of the hormone). This formed the basis for specificity in future hCG immunoassays.
In 1976, the first home pregnancy tests became available. These earliest home tests were more accurate for positive results than for negative, and required two hours before results could be read.
Throughout the 1980s, 1990s and into the 21st century, home pregnancy testing has improved considerably with the development of new antibodies, and enzymes or coloured particles in place of radioactive labels. The latest immunochromatographic or lateral flow tests simply requires the woman to dip a test stick in her urine and wait a few minutes for a result. Any hCG present in the urine will bind to colour-labelled specific antibody and travel along a test strip by capillary action. Immobilised antibodies under a result window trap the colour-labelled hCG complex causing a line or positive symbol to appear. In the absence of hCG this line or cross would not appear, indicating a negative result.
Home pregnancy tests are now accurate from the first day of the missed period and empower women in the management of their pregnancy from the earliest opportunity, allowing them to receive good antenatal care and advice from the onset; to avoid infections, foods and substances that might be harmful to the developing foetus; and to ensure a healthy balanced diet with any supplements that might be necessary, such as folic acid and iron.
AAlthough a woman no longer needs to have a urine sample sent off to a laboratory in order to confirm that she is pregnant, there is still an important role for pregnancy testing in the hospital setting.
Highly sensitive, quantitative measurements of hCG in blood can be performed in laboratories and are invaluable in detecting very early pregnancy. Serial quantitative measurements are also extremely useful in identifying complications, such as ectopic pregnancies, monitoring certain conditions and confirming miscarriage.
In addition, it is important for medical professionals to ensure that a patient is not pregnant prior to certain procedures, such as X-ray, or before administrating potentially harmful medications. In emergency situations, it may be necessary to do this very quickly and so a rapid point-of-care test, such as the Clinitest® hCG Pregnancy Test may be used.
This method can detect levels of hCG as low as 25mIU/ml in less than five minutes and with greater than 99% accuracy. Also, since the result is read by the CliniTek Status Analyser, there is less opportunity for misinterpretation, ensuring consistent and reliable results.
Improved pregnancy management
Modern, rapid pregnancy tests allow women to receive the best and most appropriate antenatal care from the earliest opportunity and ensure that health professionals are fully informed prior to making important medical decisions. This can now be done in a matter of minutes; quickly and accurately; with minimum fuss; and in the privacy of home or at the patient's bedside - a far cry from the toad tests of the past!