what are the baby's fontanelles used for?

Fontanelles, these membranous spaces between the bones of the skull, are characteristic of the infant. An object of concern for parents due to their fragile appearance, fontanelles are more robust than we think. Here are 5 things to know about these dreaded soft spots.

At birth, the skull bones are not completely sutured. They are connected by junction spaces, the fontanelles, soft membranes to the touch. “There are six in all. But the most visible are the anterior fontanel located at the front of the skull, in the shape of a diamond, and the posterior fontanel at the back of the skull, smaller and in the shape of a triangle.”, Says pediatrician Dr. Emmanuelle Rondeleux.

What are they for ?

Fontanelles, making baby's skull more flexible, facilitate its passage in the basin and the vagina during natural delivery. “As we can see, some babies are born with their pear-shaped skull temporarily, which proves that the shape of their heads has adapted to the path they had to travel before reaching the world. Midwives can also check the baby's head position during delivery just by touching the fontanelles when the baby is about to go out.Explains the pediatrician.
Finally, these soft and flexible membranes allow progressive brain growth. The cranial perimeter is 35 cm on average at birth, it reaches 50 cm at the age of 2 years and 51/52 cm at 3 years. The skull continues to grow until adulthood to measure between 55 and 57 cm in diameter, its final size.



© Getty

Are they fragile?

It is often said that the baby's fontanelles are fragile… wrongly! It is true that the fact that they are soft gives them a delicate appearance. But they can completely be handled without danger for the infant, on condition of doing it delicately obviously. “Under the fontanelles are the meninges. The outermost of the three meninges is called the dura mater. As its name suggests, it is relatively solid because its membrane is thick. We can therefore pet the fontanelles without problem and massage the head of the newborn to wash his hair. Just as if the child has crusts of milk at the level of the anterior fontanel, parents should not hesitate to peel them off as they would elsewhere on the skull ”, reassures the specialist.

When do they close?

All babies are born with six fontanelles. Four of them close during the first days of life. The two remaining ones, the posterior fontanelle (small fontanelle) and the anterior fontanelle (large fontanelle), will close over the months. The suture of the posterior fontanel is done on average between 2 and 3 months. The anterior fontanel, which measures between 2 and 3 centimeters wide, closes between 9 months and 2 years, “most often between 15 and 18 months”, Points out Dr. Rondeleux. These figures are averages, the ossification of the fontanelles varies from one baby to another.

Can the appearance of fontanelles be a sign of a problem?

Some parents are concerned when their baby's front fontanel bulges or moves at the same rate as the heartbeat. Be aware that it is normal for the fontanel to take on a bulging or "beating" appearance when the child cries, cries or coughs. This change of form is safe when it is temporary. On the other hand, a fontanelle which remains bulged is a reason for consultation with a doctor because it can be the sign:

  • of a intracranial hypertension or hydrocephalus, that is, the presence of fluid in the brain. “If it is an external hydrocephalus, it does not matter because it resolves by itself. But it must be monitored by a health professional”.
  • of a meningitis.


If meningitis or intracranial hypertension is suspected by a doctor, a transontanellar ultrasound can be performed to explore the intracranial contents. This is possible as long as the anterior fontanel is permeable in infants. It's also "the method of choice for the first brain assessment and follow-up in premature babies", Explains the Francophone Society of Pediatric and Prenatal Imagery (SFIPP) on its website.
Conversely, a widening fontanel can be a sign of dehydration. “When dehydrated, the child has other symptoms such as diarrhea, vomiting, dark circles around the eyes and scanty urine ”, points out Dr. Rondeleux.

Is the evolution of fontanelles monitored by pediatricians?

Just like the weight and the size, the fontanelles are supervised by the pediatrician during the compulsory medical examinations. At each examination, the specialist ensures that the child's cranial perimeter is in the official curves corresponding to the age of the baby. “The sutures of the fontanelles are monitored by measuring the cranial perimeter. If there is an overlap in the sutures, the fontanelles have closed prematurely. It is a craniosynostosis, a problem that requires surgery to allow normal development of the skull.”.
A late closing of the fontanelles can be a sign of a deficiency in vitamin D, essential for the calcification of bones.

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