Why more male than female newborns may get the crucial vitamin K shot

Female newborns may be missing out on potentially lifesaving vitamin K shots more often than male newborns, according to a study of a Philadelphia health system.

Among babies born at three hospitals affiliated with the University of Pennsylvania, female newborns were less likely to receive vitamin K than male newborns, researchers report June 15 in JAMA Network Open. The apparent reason: Parents cannot get male babies circumcised at the hospitals if they refuse the vitamin K shot, which helps prevent bleeding.

The research team, from Children’s Hospital of Philadelphia, analyzed medical records for more than 93,000 infants born from 2018 to 2025. There was a big drop overall in receipt of vitamin K at birth, which is administered unless parents decline. But the refusals skewed toward female newborns, who made up two-thirds of the 777 infants who did not get the shot.

Among female infants, 10 newborns per 1,000 births did not get the shot in 2018, growing to 20 per 1,000 in 2025. For male infants, the rate climbed from 4 per 1,000 births to 10 per 1,000.

During the study, roughly three-fourths of the male newborns were circumcised in-hospital. For parents who would otherwise say no to the shot, wanting this procedure appears to tip the balance toward more male babies than female babies receiving vitamin K. The finding suggests there may need to be strategies for vitamin K acceptance specific to parents of female babies, the research team notes.

Vitamin K reduces the risk of developing a dangerous bleed early in life, which can be fatal. Newborns need a dose because little of the vitamin passes from the placenta to the fetus and breast milk doesn’t supply much either. Universal newborn vitamin K shots have been the standard in the United States since 1961. But misinformation about the shot and other routine newborn care has contributed to a nationwide increase in parental refusal of vitamin K.

The new study also found a decline in receipt of the hepatitis B vaccine at birth over time, with 83 percent of those declining vitamin K also saying no the vaccine. Earlier this year, a judge paused attempted federal changes to the pediatric vaccine schedule, including the elimination of the birth dose for the hepatitis B vaccine. The American Academy of Pediatrics and other medical societies still recommend this dose.