Study of 2 million newborns ties skipped vitamin K shot to higher bleeding risk

Newborns receive several routine immunizations shortly after birth. Prophylactic vitamin K is one such recommended shot. It activates several coagulation factors necessary for blood to clot properly, preventing vitamin K deficiency bleeding (VKDB), a condition that can be life-threatening. As more parents refuse prophylactic vitamin K for their children, researchers in Sweden wanted to examine trends in newborn vitamin K shots over time and any associations with infant bleeding diagnoses.

Researchers followed more than 2 million babies born in Sweden between 2003 and 2021, tracking vitamin K shot status and health risks linked to not receiving it. Although the rate of babies who did not receive the vitamin K shot remained low, the rate of skipping the shot more than doubled over the study period, rising from 0.66% in 2006 to 1.50% in 2021.

Babies who did not receive the injection were 1.5 times more likely to experience bleeding during their first six months of life and nearly three times more likely to develop bleeding in the brain (intracranial hemorrhage) than babies who received the shot.

The findings are published in JAMA Pediatrics.

A shot for better clotting

Vitamin K helps the body produce clotting proteins, including prothrombin, and enables these proteins to bind calcium properly, forming clots—a step crucial to stopping bleeding.

Newborns, however, begin life with very little vitamin K. Only small amounts are passed from mother to baby during pregnancy, breast milk naturally contains very little of it, and a newborn’s gut has not yet developed the bacteria needed to make its own vitamin K. Together, these factors leave babies especially vulnerable to bleeding.

Despite its benefits, more parents are refusing vitamin K shots for their babies as the world witnesses a rise in vaccine hesitancy, often driven by online misinformation. If parents refuse the shot or a baby has a health condition such as hemophilia, doctors offer oral drops instead: one dose at birth followed by weekly doses for 12 weeks.

However, studies have found that a single injection into the muscle is the most effective way to prevent bleeding, though oral drops also work but are less effective.

Researchers in this study wanted to investigate whether this same trend of declining vitamin K shots was happening in Sweden and, if so, whether babies were at greater risk of bleeding.

The team looked at several official Swedish health registers containing data on nearly all live births in Sweden between 2003 and 2021 among babies born at 35 weeks’ gestation or later. These records provided accurate information on which babies received the vitamin K shot at birth and allowed the researchers to track medical issues that occurred afterward. They followed each baby’s medical history for the first six months of life.

The data revealed that, of just over 2 million babies born, 24,089 did not get the standard vitamin K shot at birth. While most babies still get the vitamin K shot, the number who do not was growing. Babies without the shot faced significantly higher odds of intracranial bleeding, with the risk especially pronounced in the first 28 days of life.

Some parents opted for vitamin K drops instead of the injection. Yet infants who received drops instead of the shot still faced more than twice the bleeding risk of those who were injected. One likely explanation, according to the researchers, is that unlike a single shot, drops are given repeatedly over several weeks, leaving more room for missed or inconsistent doses.

This study reinforces a growing body of medical evidence showing why the vitamin K shot is essential for preventing bleeding in newborns. The researchers say parents and caregivers need better education about its importance and call for more research into why some parents refuse the shot and whether that choice is connected to other health decisions, such as childhood immunization.

Who’s behind this story?

Sanjukta Mondal

Master’s in Chemistry. Freelance science journalist and communicator. Published in Chemistry World, BioSpace, and The Hindu.

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Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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