Fontanelles in the newborn: what are they? when do they close?

When a baby is born, the skull is made up of cartilaginous bones joined by a flexible tissue, so that during labor the  baby’s head can somewhat “deform” in order to pass through the birth canal.

Despite this, the skull is very strong as well as elastic, and capable of withstanding considerable pressure due to the uterine contractions of labor.

Generally, within a few days after childbirth, the bones of the skull readjust and the head returns to its normal shape. However, small gaps remain between the bones which are called FOUNTAINS.

They serve not only to allow the bones of the skull to overlap during labor but also to give the braincase the possibility to grow continuously following the increase in volume of the brain.

In the first year of a child’s life, the brain mass increases considerably  from 350 to 700 grams and the head circumference on average goes from about 35 to 48 centimetres.

This growth slows down after the first year of life and will take about twenty years to reach 60 cm in adulthood.

How are fountains made?

The  anterior  fontanelle is located above the head while the  posterior one  towards the nape of the neck between the occipital bone and the two lateral bones. It is very small and is rarely identified as it is usually a few millimeters in size.

The anterior fontanelle usually has a diamond-like shape. It measures 2 to 5 cm in length and 2 to 4 cm in width.

When do they close?

The closure of the fontanelles consists in their transformation into bone tissue which occurs at different times in children.

The anterior fontanelle may close between 9 and 18 months. The front one within the fourth month of the child’s life.

The larger the head circumference the longer it takes to close.

Until they close they continue to pulsate following the rhythm of the heartbeat and it is noticeable in those children who are born without hair.

Are they delicate?

Yes, but not very fragile. The membranes that make them up are more resistant than we might think. We can touch it but it’s good to protect the child from bumps.

When the baby cries, it may happen to see the fontanelle swell slightly until it is on the same level as the surrounding bones. And this is normal. Instead, it is advisable to notify the pediatrician if they swell and the child has a high fever or if they are sunken and the child is suffering from vomiting and diarrhea: in this case, depression of the fontanelles could signal ongoing dehydration.