A new study claims to reveal how the hormone pregnancy test drug Primodos damages the foetus in some pregnant women.

The report comes after alleged victims of the drug had their legal challenge against the manufacturer and the Department of Health struck out by a judge in May this year.

Primodos was a hormone-packed pill and, in the 1960s and 70s, GPs gave it to women to test whether they were pregnant.

This new report produced by a Swedish professor of pharmacology and toxicology claims the drug could cause damage to the foetus in similar ways to abortion drugs.

Bengt Danielsson, who has worked in the field of drug safety and teratology for 35 years, spent two years analysing data from studies on Hormone Pregnancy Tests (HPTs), concluding the drug had the potential to cause a range of congenital problems, such as shortened limbs, skeletal malformations, and cardiovascular defects.

Campaigners plan to raise the findings in a meeting on Wednesday with the minister for patient safety, who agreed to look again at the issue following a heated debate in parliament in September.

Previously, the government had apologised for letting down the alleged victims of Primodos, before siding with the manufacturer to block their legal claim.

HPTs were sold under different trademarks, the most prevalent in the UK was called Primodos.

Unlike the urine pregnancy test that was developed later, these were two pills that were handed out by GPs to be taken 12 hours apart.

This would give the woman a rise in hormones, followed by a rapid decline, mimicking the end of the menstrual cycle, which in non-pregnant women would trigger a menstruation bleed.

If a pregnant woman used HPTs, she would generally have high levels of pregnancy-induced progesterone, which maintains pregnancy normally and there is no bleed – and this is how the woman knows she is pregnant.

However, Professor Danielsson’s study suggests that HPTs have potential for a third outcome – to initiate a failed abortion process, resulting in uterine contractions and bleeding in some pregnant women – most likely those women with naturally lower progesterone levels when pregnant.

He argues the hormone spike from the pregnancy test could give women with low progesterone levels uterine cramping, resulting in the womb attempting to expel the uterine lining with the living embryo.

His paper suggests this also decreases blood flow to the embryo, starving tissues of oxygen (hypoxia) and when the oxygen returns, this can also impact recently formed blood vessels within the embryo (so called “vascular disruption”) which can damage whatever is developing at the time.

This could range from shortened limbs to hand defects – to damaged internal organs such as the heart and brain.

Professor Danielsson argues this “vascular disruption” is the same mechanism that can occur with the morning-after pill, Misoprostol, if it somehow fails to abort the embryo.

He says his hypothesis is supported by numerous factors, not least results in a human clinical trial in Australia, where a proportion of women who used HPTs showed “spotting” and signs similar to an early threatened miscarriage.

He also notes that the types of malformations seen in alleged HPT victims are near identical to those associated with Misoprostol.

He told Sky News: “Depending when in pregnancy of having this hypoxia, the oxygen deficiency event, that also tells you what type of malformations you would get.

“So, if it’s early on, it would be more severe, for example an amputation of the arm. Later, it might be the branches of the latest developed vessels such as the fingers.”

Professor Danielsson is also critical of an expert working group EWG commissioned by the British government, which concluded in 2017 that they could not find evidence to prove a causal association between hormone pregnancy tests and malformations in the embryo.

He argues that the datasets within the annexes of their report show the association exists.

He said: “One of the annexes to the EWG report, highlighted that HPTs may cause embryonic hypoxia by a similar mechanism as Misoprostol and that several types of malformations associated with HPTs were of the same ‘vascular disruption’ type as shown for Misoprostol.”

He added: “Two extensive epidemiogical investigations on HPT-associated malformations, based on totally different populations and different methods, were presented in annexes to the EWG report.

“Both showed consistency in increases of several specific defects, however this important aspect was neglected.”

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Charles Feeny, the barrister who represented the alleged victims of Primodos, said: “It was like they (the EWG) had the pieces of a jigsaw on the table – and it’s a complicated jigsaw and you’ve got to put the pieces together carefully and they just weren’t able to do that.

“What Bengt Danielsson’s done is put all the pieces together – and there you can see that clear picture.

“Hormone Pregnancy tests did cause malformations, but they caused them in a small group of women, the women who were susceptible to it, probably because they had low progesterone levels, even though they were pregnant.”

Mr Feeny also believes the drug would have caused some women to have abortions.

The High Court judgment in May dismissed the legal case in the UK. Previous litigation against Schering, which is now owned by German manufacturer Bayer, also failed in 1982 when the claimants’ legal team decided to discontinue on the grounds that there was no realistic possibility of success.

Bayer told Sky News: “Since the discontinuation of the legal action in 1982, Bayer maintains that no significant new scientific knowledge has been produced which would call into question the validity of the previous assessment of there being no link between the use of Primodos and the occurrence of such congenital anomalies.

“In 2017, the Expert Working Group of the UK’s Commission on Human Medicines published a detailed report concluding that the available scientific data from a variety of scientific disciplines did not support the existence of a causal relationship between the use of sex hormones in pregnancy and an increased incidence of congenital anomalies in the new-born or of other adverse outcomes such as miscarriage.

“The Committee for Medicinal Products for Human Use of the European Medicines Agency supported that conclusion.”