by Margaret Sparrow
Human Chorionic Gonadotropin (hCG), is a pretty special hormone excreted by the placenta to maintain a pregnancy. It can be detected in blood at low levels and also less sensitively (but more conveniently) in urine, especially that first morning sample when urine is more concentrated. There are two subunits (alpha and beta) and it is the beta subunit which is used in most pregnancy tests.
Immunologic tests are so called because hCG is an antigen which can trigger the production of antibodies. It is these antigen-antibody reactions which are the basis of various tests. Some tests depend on the detection of antigen, others the antibodies.
The door to immunologic pregnancy tests was opened in 1960 when two Swedish researchers (Wide and Gemzell), published the results of a technique called haemagglutination inhibition which detected antibodies to hCG. It was done in a test tube using red blood cells from a sheep which clumped together (agglutinated) in a special pattern when urine containing hCG was added. It took 60-90 minutes to read and was very accurate when taken one week after a missed period. Amazingly, Leif Wide made this discovery when he was a medical student studying under Dr Gemzell. As early as 1961 the method was introduced into Uppsala University Hospital. In 1962 a similar test used a drop of urine on a slide. Instead of red blood cells, latex particles were used to demonstrate the clumping pattern.
Initially tests were done in laboratories, then in doctors’ surgeries, then eventually in the privacy of home. Organon in Holland was the first to patent a home pregnancy test kit in 1969 and during the 70s these were gradually introduced elsewhere. The first home tests were pretty unreliable and one looked more like a child’s chemistry set with its vial of purified water, an angled mirror, a test tube, an eye dropper and red blood cells taken from a sheep. It took until 1971 to have home tests available over the counter in Britain, Europe and Canada, until 1977 in USA and later still in NZ in 1980.
During the 70s and 80s many innovations were marketed with the aim of making the tests more user friendly – simpler, less expensive, more convenient, and more accurate earlier in the pregnancy. A giant leap forward was the use of coloured dyes which bonded to the antigen or antibody and travelled to the test and control zones which appeared like magic as coloured lines. Instead of test tubes or slides we were enticed by elegant test kits or a strip or wand to hold in the stream of urine.
Another significant advance was the introduction of quantitative tests which measure the level of hCG in International Units/ml. Quantitative tests have many other uses but as far as abortion is concerned they are very useful in determining whether the abortion has been successful. Levels will remain higher than expected if there is an incomplete abortion with pregnancy tissue remaining or if there is a continuing pregnancy. Women are advised to have a post-abortion check in about 2 weeks. At this time a free blood test is available through a laboratory or a low sensitivity test can now be provided to do at home at a reasonable price. This test will only be positive when the level is over 1000 International Units/ml. It is very useful now that early medication abortion can be provided by telemedicine. (Thanks to the law changes!)
Compared to the rapid uptake of rapid antigen tests for Covid, why did it take so long for pregnancy self-testing to become available? The problem was not the tests but judgmental attitudes. Could women really be trusted to carry out instructions? Wasn’t it better to have the diagnosis from a doctor? What about false negatives and false positives? Women would not understand about reliability. What about counselling? What about support if the result was not the desired result? What about privacy? Who should provide the tests – doctors, laboratories, pharmacies, family planning clinics, mail order? And so on….
It was a coincidence that the introduction of pregnancy testing came at the same time as the sexual revolution of the 60s to 80s. This was a time of great social change which came to be associated with permissiveness (free love), women’s liberation, abortion law reform, gay rights and the erosion of medical authority. Self-testing gave women greater autonomy and contributed to a realignment of the power dynamics between doctors and patients. The humble pregnancy test sits alongside the birth control pill introduced in NZ in 1961 as a significant agent of change.
Dame Margaret Sparrow was a medical doctor, abortion provider, and president of ALRANZ for many years.