Components of a hormone pregnancy test used in the 1960s and 1970s can cause deformities in fish embryos, a new Aberdeen University study suggests.

Hormone pregnancy tests (HPT) were given to an estimated 1.5 million women in the UK between 1958 and 1978 to determine whether or not they were expecting.

The tests, which contained the hormones progestogen and oestrogen, were withdrawn from the market in 1978.

Studies from the late 1960s suggested a link between use of HPT and a wide range of serious birth defects.

However, a recent review into the tests concluded the scientific evidence "does not support a causal association" between the use of HPTs, such as Primodos, and birth defects or miscarriage.

The new study found how after components of the drug were added to water around zebrafish embryos, their movement slowed down rapidly and developed changes to the heart within four hours.

Within 24 hours it displayed damage to tissues such as the fins, eyes and spinal chords and it suggested that the drug accumulates in the embryo over time.

Researchers say that if this also occurs in a mammalian species, that even a low dose of the drug for the mother could result in much higher levels for the embryo.

Research leader Dr Neil Vargesson said: "At the moment the scientific research into whether or not Primodos caused these birth defects is inconclusive.

"Our experiments with the zebrafish embryos shows quite clearly the effects the Primodos components have - this does not mean it would do the same in humans of course, but we need to carry out more research into these components.

"The assumption by some previously has been that the doses given to mothers was too low to cause any damage but our study shows that the levels of Primodos' components accumulate in the embryos over time because they don't have a fully functional liver that can break down the drug."

Dr June Raine, director of vigilance and risk management of medicines at the Medicines and Healthcare products Regulatory Agency, said: "The Commission on Human Medicines conducted a comprehensive independent scientific review of all available evidence including this then-unpublished scientific study.

"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."