"Test tube" babies are more likely to be premature and have a low birth weight, but it's unlikely that assisted reproductive technology is the reason why, researchers say.
Their findings challenge the widely held belief that procedures such as freezing embryos, the delayed fertilisation of eggs and hormonal treatments lead to these problems.
"These findings will reassure prospective parents and medical professionals that the (assisted reproduction) techniques per se appear unlikely to substantially increase the risks of poor birth outcomes," said study leader Alice Goisis, of London School of Economics and Political Science.
More than five million children have been born through in-vitro fertilization (IVF) and other assisted reproduction techniques, the researchers noted.
They compared data on siblings who were conceived naturally and conceived through assisted reproductive technology (ART). They used records on more than 65 600 children born in Finland between 1995 and 2000.
On average, siblings conceived through ART had a higher risk of premature birth and low birth weight, they found.
But after further analysis, this increased risk became negligible or vanished, suggesting that factors other than ART were responsible for those birth problems, the authors said.
Parents' health and mental stress associated with fertility problems, genetics, and birth order were among the possible contributing factors.
About 60% of children born through ART are first-born, which is also a risk factor for birth problems, the researchers noted.
"As a group, children born after (ART) are, in absolute terms, at increased risk of adverse birth outcomes. But the results of the current study indicate that this elevated risk is likely attributable to factors other than the treatment itself," Goisis and colleagues said in a school news release. But the study did not prove that ART played no part in birth complications.
"Understanding the risks associated with (ART) treatment is very important," they added.
The study was published in The Lancet.
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