Waiting three minutes or longer before clamping a newborn’s umbilical cord reduces the prevalence of iron deficiency at four months, a large trial has found.

Swedish researchers studied 334 infants, randomly assigning half to have their cords clamped within 10 seconds of birth and the rest to clamping after three minutes or longer. The two groups were statistically identical in gestational age, head circumference, health and age of the mother, and other characteristics.

In blood tests at two days after birth, there were no significant differences in iron status. But when researchers analyzed blood taken at four months, they found iron concentrations were 45 percent higher in the delayed clamping group, and iron deficiency was significantly more prevalent in those who were clamped early.

Dr. Ola Andersson, the lead author and a pediatrician at the Hospital of Halland in Halmstad, Sweden, pointed out that there were no adverse effects to delayed clamping.