Researchers at the University of Copenhagen, Denmark, compared birth data from 92,000 twins and singletons born following fertility treatment between 1988 and 2007 in Norway, Sweden, Denmark and Finland with data from babies conceived naturally. It is one of the largest long-term studies into the health of babies born following ART, including IVF, ICSI and embryo transfer.
As well as a decline in the rate of stillbirth and infant death, preterm delivery and low birth weight among ART singletons, the study also showed that fewer ART twins were stillborn or died in infancy than twins who were conceived naturally.
Dr Anna-Karina Aaris Henningsen, who was involved in the research, said: 'During the 20-year period of our study, we observed a remarkable decline in the risk of being born preterm or very preterm.'
'These data show that if there is a national policy to transfer only one embryo per cycle during assisted reproduction, this not only lowers the rates of multiple pregnancies, but also has an important effect on the health of the single baby,' she added.
Further analysis from the study shows the proportion of babies born preterm - before 37 weeks of pregnancy - fell from 27.9 percent between 1988-1992 to around 13 percent between 2003-2007 in Sweden. In Denmark, Finland and Norway it decreased from a similar starting figure to 21.1 percent, 17.8 percent and 21 percent respectively.
Rates of ART singletons born small for gestational age more than halved between 1988-1992 and 2003-2007, falling from 7.6 percent to 3.2 percent. Over the same time period, ART twins born small for gestational age fell from 17 percent to 14 percent.
While this study highlights an improvement in health outcomes for babies conceived using ART, other factors than a rise in single embryo transfer may have contributed to outcome, such as advances in ART and improved treatment protocols.
Dr Henningsen says: 'We have improved both the technical skills in the laboratory and the clinical skills of the doctors and also perform milder ovarian stimulation.' She concludes 'the most important reason is the dramatic decline in multiple births due to policies of choosing to transfer only one embryo at a time'.
The ART multiple birth rate in the UK has fallen from 25 percent in 2008 to 16 percent in 2013.