Why Do Newborns Need the Vitamin K Shot?

The vitamin K shot is one of the most effective preventive measures in newborn care. Without it, newborns face a serious risk of vitamin K deficiency bleeding (VKDB)—a rare but potentially fatal bleeding disorder that can strike in the first six months of life. A single injection at birth eliminates nearly all of that risk.

Newborns arrive with almost no vitamin K stored in their bodies. Vitamin K is the nutrient that allows blood to clot—without it, the body cannot stop bleeding, from minor wounds to, in rare but serious cases, bleeding in the brain.

“Without vitamin K, our blood cannot clot, and if we supplement babies with vitamin K at birth, we can prevent serious bleeding,” explains Jaspreet Loyal, MD, MS, a Yale Medicine pediatric hospitalist. “In time, an infant’s gut microbiome develops and is able to make vitamin K as they are eating and growing, but this deficiency exists at birth.”

Vitamin K is a fat-soluble nutrient essential for blood clotting and bone health. Older children and adults get it from leafy greens, dairy, eggs, and meat. Healthy bacteria in the intestines also produce it.

Newborns, however, start life with very little. Vitamin K does not cross the placenta in meaningful amounts, and breast milk—while beneficial in countless other ways—does not supply enough to meet an infant’s clotting needs. Formula-fed babies are somewhat better off, since formula is fortified with vitamin K, but the shot remains the standard of care for all newborns regardless of feeding method.

Vitamin K deficiency bleeding, or VKDB, is a rare but serious condition in which a newborn’s blood cannot clot properly. It can cause bleeding anywhere in the body—including the brain—and can cause permanent injury or be fatal.

There are three types, defined by when they occur:

• Early-onset VKDB appears within the first 24 hours after birth. It is usually associated with mothers who took certain medications during pregnancy that interfere with vitamin K, including some anti-seizure and blood-thinning medicines.
• Classical VKDB occurs between 2 days and 1 week after birth. Early and classical cases together affect approximately 1 in 60 to 1 in 250 newborns who do not receive the shot.
• Late-onset VKDB occurs between 1 week and 6 months after birth, affecting approximately 1 in 14,000 to 1 in 2,000 unprotected infants. It is the most dangerous form and most likely to involve brain bleeding.

Symptoms range from easy bruising or bleeding from the nose or umbilical cord site to severe internal bleeding. Infants with severe VKDB may spend weeks in the hospital, including in intensive care.

Infants who do not receive the vitamin K shot are 81 times more likely to develop late-onset VKDB than those who do.

Yes. The vitamin K shot has been a routine part of newborn care in the United States since 1961 and has an extensive safety record.

Side effects are uncommon and mild: minor bruising, brief pain, or slight swelling at the injection site. The shot is given in the thigh. Vitamin K is then stored in the baby’s liver and released gradually over the following months.

Most formulations contain a small amount of benzyl alcohol as a preservative. For families who prefer it, Yale New Haven Hospital carries preservative-free vitamin K as well.

The shot is given before the baby is discharged from the hospital. Most hospitals, including Yale New Haven Hospital, prioritize uninterrupted skin-to-skin time between the parent and newborn in the first hour after birth, so the shot is not given immediately upon birth, notes Dr. Loyal, calling it “the golden hour” for the parent of a healthy newborn.

“After that early bonding, we usually bring the baby over to the warmer or bassinet to get assessed by a nurse or doctor and can give the shot then, usually along with an eye ointment to prevent neonatal bacterial conjunctivitis,” she says.

If a family wants to delay the shot slightly, that is generally fine so long as it is given before the baby goes home. For boys having a circumcision, the shot must be given beforehand.

Parents worried about their baby’s discomfort during the injection can ask to hold and nurse the baby during the shot, which may help.

“We tell parents that with any injection, there is potential for discomfort or pain, but that’s all,” Dr. Loyal says.

Newborns typically receive other preventive treatments around the same time, including the hepatitis B vaccine and, more recently, an antibody injection to protect against respiratory syncytial virus (RSV).

Some countries give vitamin K to newborns orally rather than by injection. This approach is not approved by the U.S. Food and Drug Administration (FDA), and the evidence suggests it is less reliable.

“Surveillance studies in countries that do this have shown that there are cases of vitamin K deficiency bleeding even with the oral administration, whereas if you give the injection, there are zero cases,” Dr. Loyal says.

Vaccine and shot hesitancy has increased in recent years. According to research published in JAMA, refusals of the newborn vitamin K shot rose nearly 80% in the United States between 2017 and 2024. Pediatricians at Yale Medicine are trained to approach these conversations without judgment.

“Parents today feel like they have to filter through so much information; my ask is that they trust their pediatrician,” Dr. Loyal says. “We know that trust is the number one aspect of decision-making when it comes to injections and vaccines. If parents choose to go a different route, it’s important we have a conversation about it.”

Dr. Loyal advises colleagues in training to approach hesitant parents with openness rather than pressure. “I advise them to go in with curiosity, and to ask parents what they are worried about,” she says. “And I hope that parents can also be forthcoming because we are all on the same team and want to make sure the infant has the best health possible.”

If you have questions about the vitamin K shot or any newborn procedure, the best step is to raise them with your pediatrician or the care team before or shortly after delivery—so that any concerns can be addressed before decisions need to be made.