Hormone based pregnancy testing drugs (HPTs) were introduced in the 1950s. Before that time any way of testing pregnancy was primitive and unreliable. The most commonly used pregnancy test involved injecting a woman’s urine into a toad. It is not surprising that the pharmaceutical companies sought to develop a more reliable and accessible test.

HPTs were supposed to operate in a simple and safe way. The HPT consisted of synthetic hormone. If there was a pregnancy then this synthetic hormone would bind with the natural hormone progesterone protecting the foetus. Nothing noticeable would happen. However, if the woman was not pregnant then the uterus would react to the synthetic hormone in a similar way as menstruation producing a withdrawal bleed.

However, from the outset doubts were expressed about the safety of HPTs. One prescient observer writing in The Lancet referred to “the delicate balance of hormones in the uterus” doubting the safety of HPT,s. Anecdotal evidence began to emerge suggesting that HPTs were causing miscarriages and birth defects.

The first scientific study published identifying birth defects after HPT use was in 1967 based on work by Isabel Gal. The Committee of Safety of Medicines had just been established as a result of the Thalidomide scandal. The Committee, in particular its Chair Dr Inman, accepted Dr Gal’s research.

However, it appears that they were wary of confirming officially that HPTs caused birth defects .The same synthetic hormones were used in the contraceptive pill which was now gaining widespread use. There was a fear that if they indicated that HPTs were unsafe then a number of women would cease to use the contraceptive pill which was a significant advance in women’s health. HPTs were not banned for use in pregnancy in the United Kingdom until a decade later. The Cumbeledge Review which reported on HPTs in 2020 indicated that they should have withdrawn from the market as a test for pregnancy in 1967.

By the late 1970s a victim group had been established. Litigation was commenced. The manufacturers of the most commonly used HPT, Primodos, Schering, now Bayer Pharma, denied that there was any risk from HPTs. Over a period of time a number of experts appeared to change their view and supported the position of the manufacturers Most conspicuously, Dr Inman who had previously described himself as being “defenceless” in relation to HPTs was prepared to act as an expert witness in litigation for Schering. The claims were discontinued when Legal Aid was withdrawn in 1982.

A victim group continues to the present day attempting to establish what they regard as truth and justice. If you are interested in reading more, then there is a lot of information in the publication by the Group “A Bitter Pill: Primodos, the Forgotten Thalidomide”.

I first became involved in 2014 when a solicitor then acting for the victim group just asked me to take a look at the voluminous information available . My clear impression was that there was undoubtedly “something in it”. However, I was not really sure what. Whilst there had undoubtedly been a cover up, this may simply have been because of the delay in withdrawing the drug from the market. It did not follow that the HPTs did in fact cause birth defects. I was also uncertain as to why if HPTs did cause birth defects there were not many more cases as seen in Thalidomide.

Over the next decade I have advised the victim group. In 2019 the victims were encouraged when a law firm now called Pogust Goodhead agreed to take on their claims. They were disappointed when Pogust Goodhead withdrew funding. In 2023 an action initiated by Pogust Goodhead was struck out by the High Court essentially because the Claimants did not have funding to continue.

This was even though the Claimants had supportive expert evidence. Professor Carl Heneghan of Oxford University had conducted an epidemiological meta‑analysis which showed a clear association between HPTs and birth defects. His study was endorsed by independent expert evidence from Professor Maurice Zeegers of the University of Maastricht .
Professor Bengt Danielsson of the Karolinska Institute in Stockholm had provided teratological evidence that birth defects likely resulted from vascular disruption at the time of the taking of the HPT.

At this stage everything seemed finally lost. However, it transpired that Professor Danielsson had been working on the issue in his own time and without payment. Professor Danielsson with co-authors including Professor Neil Vargesson of the University of Aberdeen has now been published in two international peer reviewed journals

Reproductive Toxicology Vol 122 December 2023 1088488
Birth Defects Research Volume 117 March 2025 Issue 3

These papers show to a high degree of probability that HPTs did cause birth defects. Professor Danielsson identifies a failed abortion mechanism. Critically, the pattern of defects shown with the HPTs is the same as those caused by drugs such as Misoprostol, the morning after pill. Misoprostol and similar drugs are taken to induce an abortion. However, it is known that this does not always work. In cases in which women proceed to birth having taken the morning after pill it is now scientifically acknowledged that there is an increased incidence of birth defects. It is easy to understand that if a drug initiates an abortive process this would be damaging to a surviving foetus.

Whilst HPTs at standard doses were not intended to cause abortions, it is known that some women took excessive doses so as to result in a miscarriage. Further, it is now known significantly that some women whilst pregnant have progesterone levels lower than that of non-pregnant women. Low progesterone the natural hormone which protects the foetus would make it vulnerable to an abortive process. Appreciating this answered the doubt in my mind as to why there were not more cases. That a small proportion of women taking HPT’s were at risk is consistent with Carl Heneghan’s study which shows a modest increase in risk certainly by comparison with Thalidomide. The increase in risk is consistent across the studies .

The work of Bengt Danielsson has been reported on by Sky News.

To describe the performance of UK regulators in relation to HPTs as lamentable does not do them justice. It is far worse than that. This continues the Committee on Safety of Human Medicines part of the MHRA recently reviewed Professor Danielsson’s first paper. They described it as a “interesting hypothesis” but that it did not represent significant new evidence.

The intention is that further research should be present to the Government with a clear request that this be reviewed independently of regulators who appear intent only on defending their own position.