Experts say that delaying clamping the cord causes the baby to receive more blood from the placenta, increasing iron storage.
Previous studies have found that preterm newborns may benefit from delaying clamping of the umbilical cord. For instance, in December 2014, Medical News Today reported on a study published in the journal Pediatrics that found delaying cord clamping by 2 minutes results in better development for the newborn during the first days of life.
However, the new study is the first to assess long-term outcomes for children whose cords were not clamped immediately at birth.
Currently, the World Health Organization recommends delaying cord clamping for at least 1 minute.
Dr. Heike Rabe, neonatologist and senior lecturer at the Brighton and Sussex Medical School in the UK, who wrote an editorial to the new study - and who has conducted previous studies on the effects of delaying clamping the cord of preterm infants - says that there is "growing evidence from a number of studies that all infants, those born at term and those born early, benefit from receiving extra blood from the placenta at birth."
She explains that if there is a delay in clamping the cord, the baby receives more blood from the placenta - increasing the child's blood volume by up to a third. Dr. Rabe says this extra blood increases iron storage, which helps brain development:
"The extra blood at birth helps the baby to cope better with the transition from life in the womb, where everything is provided for them by the placenta and the mother, to the outside world. Their lungs get more blood so that the exchange of oxygen into the blood can take place smoothly."
Children in the study were followed up at the age of 4
In the new study, 263 full-term babies were randomized to either have their cords clamped immediately or have their cords clamped after 3 minutes.
At the age of 4, the children were followed up by the researchers, who tested IQ, motor skills, social skills, problem-solving, communication and behavior.
The authors report that, although girls in the study did not show any significant differences across the two groups, boys in the delayed clamping group showed modestly higher scores for social skills and fine motor skills.
Dr. Rabe speculates that girls may receive extra protection through higher estrogen levels in the womb than boys, which could explain why there was little difference between the girls in the study.
The authors write that one limitation of the study could be a possible bias in the overall development of the children whose parents chose to return to the follow-up, but remind that any limitations in study design "must be weighed against the novelty and originality of the study; this study is the first, to our knowledge, to assess the effects of delayed vs early [cord clamping] on neurodevelopment after 1 year of age."
While recent research indicates that there is no increased risk of blood loss to the mother from delayed clamping, studies have not yet determined whether there may be associated adverse outcomes to the babies, such as increasing risk for jaundice, polycythemia and high red blood count.