A new study has found that hormone pregnancy tests had the potential to deform embryos in the womb.
The controversial drug Primodos, used by women in the 1960s and 70s, was removed from the market in 1978 after concerns were raised about the drug.
But new research produced by Dr Neil Vargesson from the Institute of Medical Sciences in Aberdeen University is at odds with a recent Government-commissioned report, published three months ago, which suggested there was not enough scientific evidence to demonstrate a causal association between the drug and malformations.
Dr Vargesson's study, first seen by Sky News last year in its early stages, was published on Tuesday in The Scientific Reports.
It shows that when the drug is applied to zebra fish embryos they suffer a range of deformities, including shortened tails, spine, fin and eye defects.
Fish are often used to screen drugs as their embryos can replicate the reaction of humans. For example, Thalidomide shortens the fins in fish as it does the limbs in humans.
Dr Vargesson also found the drug caused greater damage the earlier in development the embryo is exposed to it, and that higher doses can be lethal.
He told Sky News: "With the paper we show that you get damage to tissue in areas all across to body - the fins, the ears the eyes, the spinal cord.
"We show that it is in a dose dependent manner and a time dependent manner. If you add low doses you don't get any effect but high doses can be lethal and there are doses in between that can cause damage, but the embryos survive."
He added: "Obviously with a hormone pregnancy test women are going to be taking this at different time points - so the earlier they took it there would be more damage.
"What this study says is there is a potential chance that a Primodos-type mixture could cause some problems, so more work is needed to make a final definitive conclusion.
"These poor people have been waiting 40 or 50 years to know the answer and we don't know the answer but I don't think anyone can put their hand on their heart right now and say it did not do this."
The Government's Commission On Human Medicines (CHM), set up by the Medicines and Healthcare products
Regulatory Agency (MHRA), had seen the preliminary findings of Dr Vargesson's study.
In their report, published in November 2017, they did not respond to the findings as they had not been peer-reviewed or published.
The CHM report frequently mentions that the studies available on Primodos were conducted decades ago and used outdated methodology.
They were therefore criticised by alleged victims for not giving more weight to Dr Vargesson's work, or waiting for it to be published.
Dr June Raine, MHRA's director of vigilance and risk management of medicines, said: "The Expert Working Group (EWG) of the Commission on Human Medicines conducted a comprehensive independent scientific review of all available evidence including this then-unpublished scientific study and their overall conclusion was that the available scientific evidence, taking all aspects into consideration, did not support a causal association between the use of Hormone Pregnancy Tests such as Primodos during early pregnancy and birth defects or miscarriage.
"The EWG made a number of future-facing recommendations and our focus is now on implementing these.
"While the review cannot take away from the very real suffering experienced by the families involved, it helps shape the path to further strengthen the scientific evidence which supports safety monitoring of medicines in pregnancy."
The manufacturer Schering, now owned by Bayer, has always denied that Primodos could be damaging.
A spokesperson for Bayer said: "Dr Vargesson concludes that his research data demonstrate that the active substances of Primodos are 'potentially teratogenic' (an agent that could disturb embryo development) in the zebrafish and that his findings are worthy of further research in mammalian species.
"In particular, he does not conclude that his data show that Primodos is teratogenic in humans. He rightly notes that it is 'difficult and dangerous to directly compare drug action(s) between species', a point emphasised by the EWG as well."
Marie Lyon, chair of the association for Children Damaged by Hormone Pregnancy tests, said: "The results of Neil Vargesson's research have finally exposed the dangers of the components of Primodos.
"His research will call into question the conclusions and recommendations of the EWG Report published last year. We will continue in our battle to expose the truth about HPT's and owe a huge debt of gratitude to Neil."