What are fontanelles?

22nd July 2020

Fontanelles are the gaps between a baby's cranial bones that help the baby exit the birth canal unharmed. They close over as the baby grows.

During birth the baby descends through the birth canal and comes out by rotating on his way through the canal. This process occurs because the baby's head can mould and adapt itself to the canal, as its bones are not fused. Instead, the skull comprises several separated bones. The gaps between these bones are the "famous" fontanelles.

The skull has six fontanelles, although only two can be clearly felt. They are filled with a membranous, flexible tissue and they close over as the baby grows:

  • The posterior fontanelle is located at the back of the head, above the nape of the neck. It is triangle-shaped, measuring around 0.6 cm, and closes over in around four months.
  • The anterior fontanelle is at the top of the head, is more visible and takes longer to close over – between 12 and 18 months. It is diamond-shaped and measures around 2.5 cm at birth.

Both are soft to the touch and rise and fall in time with the baby's heartbeat. The anterior fontanelle even bulges when the baby cries, which is normal and nothing to worry about.

There are also lateral, or parietal, fontanelles that are behind the ears and cannot be felt to the touch.

As well as helping during birth, the fontanelles give the brain sufficient space to develop. That is why it is important to make sure that they do not close over much earlier or much later than recommended, which your paediatrician will monitor during regular check-ups.

To help these sutures close over correctly, we recommend supplementing the diets of babies younger than 12 months with vitamin D.

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