Three studies presented to a US fertility conference found frozen embryo babies were less likely to be premature and under weight.
Previous research has suggested this is down to only the strongest embryos surviving the freezing process.
Fertility experts said more work was needed on the issue.
A Finnish study, to be presented to the American Society for Reproductive Medicine meeting in San Francisco, found that babies born from fresh embryos were 35% more likely to be premature and 64% more likely to have low birthweight than those born from frozen.
A second study, from the University of Pennsylvania in Philadelphia, found that babies born from fresh embryos were 51% more likely to have low birthweight and were 15% more likely to die around the time of birth than those born from frozen embryos.
And research by the Royal Women's Hospital in Melbourne, Australia, found 11% of babies born from fresh embryos had low birthweight compared with 6.5% of babies born from frozen.
A total of 12.3% of babies born from fresh embryos were premature, compared with 9.4% of those born from frozen, while 1.9% also suffered death compared with 1.2% from frozen.
It is thought the results were related to the quality of the placenta, the digestive and respiratory system for the foetus. However, a British expert warns that the results are not clear cut and more research is needed before changing the system for all women.
