Part 2 -Vitamin K for Newborns: Misinformation.

By Dr. Sarah Slater, DNP, PCNP-PC, ECS Specialist

A common myth that continues to spread misinformation about Vitamin K:

“Babies have all the clotting factors they need by day eight of life, making vitamin K supplementation unnecessary.”

THIS IS NOT TRUE.

This misunderstanding traces back to a study published in 1941 that is still cited today, without proper context.

This 84-year-old study, showed that a clotting protein called prothrombin rises to normal levels by seven to eight days of life. The researchers claimed, that because prothrombin reaches "normal" levels by day eight, babies have all the clotting factors they need after the first week of life. Therefore, vitamin k supplementation is not necessary.

While this finding itself was accurate, the conclusion drawn from it was wrong. This assumption missed a CRITICAL piece of the puzzle.

What is Prothrombin?

Prothrombin is a protein made by the liver and it plays an essential role in blood clotting. But having prothrombin alone is not enough. Prothrombin must be activated in order to function, and vitamin K1 is what activates it. Without vitamin K1, prothrombin remains inactive.

So what actually happens when vitamin K levels are low?

Vitamin K activates the body’s clotting cascade. A cascade means that one step triggers the next (like a domino effect) in a series of chain reactions that ultimately tells the body to stop bleeding. If one domino of this cascade is missing, then the clotting system is defective.

An analogy I heard on the Dr. Green Mom Podcast explains this well.

Think of prothrombin as the vehicle and vitamin K1 as the fuel. You can have a perfectly good car sitting in the driveway, but without fuel, it is not going anywhere. It's essentially useless.

In the same way, newborns can have normal prothrombin levels, but without vitamin K1, that prothrombin cannot function and the clotting system cannot turn on.

Without this process, even minor stressors such as bruising or the pressure of moving through the birth canal can overwhelm fragile newborn blood vessels (it doesn't matter if your birth was "gentle"). Even babies born via cesarean section are at risk, because all newborn babies have very delicate, fragile blood vessels, and a tiny, microscopic bleed can begin and fail to stop due to insufficient levels of vitamin K1 and inactive prothrombin.

This bleeding can build silently in the background, without obvious signs of injury until symptoms suddenly appear, such as seizures or other signs of brain injury. At that point, treatment requires emergency intravenous vitamin K and more intensive interventions, which carries more risk than routine prevention, and may not fully reverse damage that has occurred.

This is why I, along with the vast majority of evidence-based healthcare providers, recommend vitamin K at birth, most commonly given as a single injection into the baby's leg. It is a simple, well-studied intervention that protects babies during a short but critical period while their own clotting system is developing.

But what if a parent does not want the vitamin K injection?

What about oral vitamin K?

In Part 3 of this series, we will address the controversy and what parents deserve to know about injection versus oral vitamin K administration.