Complications associated with IVF are due to underlying fertility problems in the parents and not the techniques used during treatment, research suggests.
A study of more than 1.2 million births in Norway found an increased risk of low birthweight, premature birth or still birth after fertility treatment.
But further analysis showed this was unlikely to be related to the treatment itself, The Lancet study reported.
Around 1.5% of births in the UK are a result of fertility treatment.
Previous research has also shown that single births after fertility treatment are associated with a higher risk of complications but the reasons have been unclear.
"It is reassuring to see that, in this study at least, the laboratory procedures were not contributing to adverse birth outcomes for those born"
In the latest study, babies born after fertility treatment were on average 25g smaller at birth, were born two days earlier and had a 31% increased risk of stillbirth.
But when the researchers looked in more detail at a subgroup of 2,500 women who had had babies naturally and through fertility treatment they found no significant difference in outcomes between the two kinds of births.
This suggests that the increased chance of complications may be due to the factors causing the fertility problems in the first place rather than the technology used to increase chances of conception, the researchers concluded.
'Reassuring'
The study excluded twins and triplets as they are known to be at increased risk of premature birth and low birth weight.
Study leader Dr Liv Romundstad, from St Olav's University Hospital in Trondheim, said the results were reassuring.
"That's good news absolutely - the technology is safe."
She added that more research was needed to better understand the reasons behind infertility which may lead to problems during pregnancy and birth.
"It could be several reasons which are hard to study, such as hormone disturbances or inherent genetic defects.
"And it could be different for each couple."
Dr Allan Pacey, senior lecturer at the University of Sheffield and secretary of the British Fertility Society, said some studies had shown an increased risk associated with some assisted reproductive techniques .
"What has been unclear is whether this was because of the underlying infertility of the parents or because of the laboratory procedures to manipulate sperm, eggs and embryos.
"Studies like this one are very important in helping us disentangle the relative contribution of these variables and it is reassuring to see that, in this study at least, the laboratory procedures were not contributing to adverse birth outcomes for those born."
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