The breakthrough follows research that allows doctors to spot early signs of embryos likely to divide into two, forming identical twins in the womb.
Most twins born through IVF programmes arise because more than one embryo is implanted into the woman. But embryos created at fertility clinics are up to seven times more likely to split into two.
Dianna Payne at the Mio Fertility Clinic in Yonago, Japan, used a high magnification digital video camera to film embryos growing from just four cells until they were a ball of cells five days old. After less than 12 hours in a culture dish, two of the embryos repeatedly collapsed upon themselves and then began swelling again. The images revealed the cells were re-arranged and formed two dark patches, which split the embryo into two, forming identical twins.
Ms Payne said that while the results are preliminary, they suggest it should be possible to spot embryos that are developing into identical twins before they are moved to the womb.
