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For most obstetricians, the best time to cut the umbilical cord is right after birth.
But a large Swedish study has found that waiting at least three minutes before clamping the cord reduces the chances of iron deficiency at four months.
The trial involved 334 infants, half of whom were randomly assigned to have their cords clamped within 10 seconds of delivery. In the other infants, umbilical cords were left to pulsate for three minutes or longer before clamping.
Iron levels in the two groups were similar two days after delivery. But four months after birth, researchers found that iron levels in the blood were 45 per cent higher in the delayed-clamping group, while infants whose cords were clamped early had increased rates of iron deficiency.
"Iron deficiency even without anemia has been associated with impaired development among infants," the researchers wrote in the study, which was published in the British Medical Journal.
Lead author Ola Andersson, a pediatrician at the Hospital of Halland in Halmstad, Sweden, noted that many obstetricians believe that delayed clamping causes jaundice. But he and his colleagues found no link between delayed clamping and jaundice, or any other adverse effects.
The Swedish research confirms what registered midwives have practised for years, says Kelly Hayes, vice-president of the Midwives Association of British Columbia. "I think they're right on the money."
Registered midwives follow scientific literature, she says, and "over and over it's been shown that there are benefits to delayed cord clamping."
In infants who require resuscitation after birth, for example, an unclamped cord provides a source of oxygen, Ms. Hayes says.
After a birth with no complications, a registered midwife may leave an umbilical cord unclamped for two minutes or up to half an hour. Not rushing the intervention allows bonding between mother and baby, she adds.
The Society of Obstetricians and Gynaecologists of Canada is more circumspect regarding the benefits of delayed clamping. "For term newborns, the possible increased risk of neonatal jaundice requiring phototherapy must be weighed against the physiological benefit of greater hemoglobin and iron levels up to six months of age conferred by delayed cord clamping," states the SOGC's 2009 guidelines.
But the Swedish researchers, whose study is the first to look at infants' iron status beyond the first days of birth, in a high-income country, were unequivocal.
"Our results suggest that delayed cord clamping also benefits infant health in regions with a relatively low prevalence of iron deficiency and should be considered as standard care for full-term deliveries after uncomplicated pregnancies," they concluded.