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Women wanting to get pregnant are encouraged to take folic acid - a natural form of vitamin B - to avoid abnormalities such as spina bifida.
But because around half of pregnancies in the UK are thought to be unplanned, the Government is considering adding it to bread.
However, experts are warning that such a move could see a leap in multiple births for those undergoing fertility treatment.
The researchers, led by Dr Paul Haggarty, from the University of Aberdeen, wrote: "Proposals to fortify the UK diet with folic acid could lead to an increase in the number of twins born after IVF".