What serious effects will delayed fontanel closure have on the baby? Fontanelles are plates of cartilage on the top of a newborn\’s head that allow a newborn\’s head to deform and fit into the birth canal during delivery. Over time, the fontanelles gradually close to protect the baby\’s brain. However, when fontanelles close too late, there can be a range of potential effects and health problems. In this article, we will discuss four serious effects that delayed fontanelle closure can have on a baby. Effect 1: Head circumference increases by 1