Transferring one embryo during each of two consecutive test tube baby treatments produces the same success rate as implanting two at once, Swedish researchers said on Tuesday.

It also cuts the risk of multiple births, they told a fertility conference here.

Many doctors transfer two or more embryos into the patient’s womb during fertility treatments in the hope that at least one will implant and result in a pregnancy.

But the practice has caused a rise in multiples births that can be dangerous for both mother and baby.

Dr Ann Thurin, of Sahlgrenska University Hospital in Sweden, presented research that showed single embryo transfer (SET) is just as successful.

“The concept of 1+1 compared with a two-embryo transfer has not been tried before and we were pleased to see that the women who had SET had an ongoing pregnancy rate nearly as high as those who had double embryo transfer,” Thurin said.

Her team studied 661 patients in 11 fertility centers in Sweden, Norway and Denmark who were having their first and second in-vitro-fertilization cycles.

One group had SET and if it was unsuccessful it was repeated a second time, while the other group had two embryos transferred during one cycle.

The pregnancy rate was 39.7 percent in the SET group and 43.5 percent in the double embryo women.

The only problem, Thurin said, is that SET patients might need to go through one additional frozen cycle (using a previously frozen embryo) in order to have the same chance of pregnancy. But that was offset by the lower risk for mothers and children by avoiding multiple births.

Thurin was speaking at the European Society of Human Reproduction and Embryology conference.