Cutting the umbilical cord immediately after birth - currently standard practice - puts the baby at risk of iron deficiency, experts say.
Official guidelines are currently being examined - and professionals and campaigners say they should change.
Leaving the cord attached for a few minutes allows the blood in the cord to transfer to the baby,
The National Institute for Health and Care Excellence (NICE) says it will publish new guidelines next year.
The existing guidance on cord-clamping was published in 2007, when the consensus was that cutting the cord immediately was the best option - something which had been the case for decades.
But since then, researchers have questioned whether that is still the case.
A paper from the Royal College of Obstetricians and Gynaecologists (RCOG) published in 2009, stated that babies whose umbilical cords are clamped immediately have lower iron stores for up to six months.
Low iron levels have been linked to brain development problems.
The suggestion is that the cord should not be cut until it has stopped pulsating naturally - anywhere between two and five minutes after birth.
Some hospitals have already changed their practice.
'No good evidence'
Commenting on the current re-evaluation of the guidance, an RCOG spokeswoman said: "The college recommends that the umbilical cord should not be clamped earlier than necessary and should always be based on clinical assessment of the situation.
"Research has shown that delayed cord clamping of more than 30 seconds may benefit the newborn in reducing anaemia.
"It also allows time for the transfusion of placental blood to the newborn, especially in cases of premature birth."
But she said there could be some cases where complications meant it was better to clamp the cord immediately.
Belinda Phipps, chief executive of the National Childbirth Trust (NCT) said: "When a baby is born about a third for the baby's blood is still in his/her cord and placenta.
"With no good evidence to support it, accepted practice is to accelerate the arrival of the placenta with an injection and clamp and cut the cord immediately, depriving the baby of this blood.
"The NCT would like to see the default position become leaving the cord for a few minutes until it stops pulsating, unless the mother chooses to have an injection to speed the arrival of her placenta or unless the blood loss from the mother means her uterus must be encouraged, with drugs, to contract and expel the placenta quickly."
Prof Mark Baker, director of the centre for clinical practice at NICE, said all its guidelines were regularly updated to take into account developments in research.
He added: "All available evidence on the right time to clamp a newborn baby's cord is being considered.
"Our recommendation will represent what we believe is best possible practice and will put mother and baby's safety first."