Clamping the umbilical cord straight after birth does not benefit mother or baby and may actually be harmful, a UK expert has warned.
Instead, leaving the cord for around three minutes can boost the baby's iron stores, cutting the risk of anaemia.
Babies born prematurely would particularly benefit from delayed clamping where it is safe to do so, a British Medical Journal paper said.
Experts recommended mothers-to-be discuss the issue with their midwife.
Early clamping is widely used as part of "active birth management" guidelines, which have been shown to prevent the mother haemorrhaging immediately after birth.
But Dr Andrew Weeks, senior lecturer in obstetrics at the University of Liverpool, said although some steps were important, there was no evidence that clamping the cord immediately had any benefit for the mother.
In the baby, evidence has shown that allowing the cord blood to keep flowing for a few minutes increases the iron stores.
In the developing world, where anaemia is a big problem, practices have now changed to delay clamping and the World Health Organization has dropped early clamping from its guidelines.
Dr Weeks, who is also a practising obstetrician, said it was time to reconsider the practice in the UK.
"It would never be implemented now if it wasn't part of standard practice, but people are reluctant to remove it because it's part of current culture.
"There is now considerable evidence that early cord clamping does not benefit mothers or babies and may even be harmful."
He recommended waiting three minutes in healthy babies but said the issue was more complicated in babies born prematurely or by caesarean section even though they would perhaps benefit the most.
"For them a policy of 'wait a minute' would be pragmatic," he added.
There have been concerns that in healthy babies delaying clamping could increase the risk of jaundice, but a recent study in the US suggested this was not the case.
Professor Andrew Shennan, spokesperson for the baby charity Tommy's, said it was not currently routine to delay clamping.
"It wouldn't be a big step not to clamp the cord for a while, and that's what nature intended.
"Asking a midwife to do that is a perfectly reasonable request - this is an area we need to look at."
Pat O'Brien, obstetrician and spokesperson for the Royal College of Obstetrics and Gynaecology, said the profession needed to go back and look at the evidence again.
"It's always been a question of risks and benefits, but time of clamping hasn't really been looked at before."
But he added there were exceptions when it would be dangerous to delay clamping because the baby needed medical support.