Fontanelle

The posterior fontanelle usually closes by the time your baby is about 2 months old. The anterior fontanelle can close any time between 4 and 26 months of age. The anterior fontanelle tends to close earlier in male than in female children.

Your doctor will touch your baby's fontanelles as part of their routine medical examination. If you run your fingers softly along your baby's head you can probably feel them. There is no need to be concerned or worried about touching your baby's fontanelles, if you are touching them gently.

Your baby's fontanelle should feel soft and flat. If you softly touch a fontanelle, you may at times feel a slight pulsation due to blood flow in the blood vessels around the brain — this is normal. If your baby's fontanelle changes, or feels different to how it usually does, show your doctor or midwife, as it may be the sign of a health problem.

Sunken fontanelle

If you notice that your baby's fontanelles are low or sunken, your baby may be dehydrated.

However, you will usually notice other signs of dehydration in your baby before their fontanelles becomes sunken.

Other signs of dehydration include:

• having fewer wet nappies
• not feeding well
• loosing fluids from vomiting or diarrhoea
• perspiration (sweating) in very hot weather (in older babies)
• being less alert or floppy

Bulging fontanelle

A bulging or swollen fontanelle may indicate rare but serious conditions including:

• meningitis or encephalitis (infections in the brain)
• cerebral haemorrhage (bleeding in the brain)
• hydrocephalus
• an abscess
• another cause of increased pressure in the brain

Your baby's fontanelles may close early. This can happen for several reasons, including hyperthyroidism (high levels of the thyroid hormone) or hyperparathyroidism (high levels of parathyroid hormone).

Another cause of early fontanelle closure is a condition known as craniosynostosis. Craniosynostosis occurs when one or more of the fibrous joints (sutures) between the bone plates in a baby's skull fuse too early, before the brain has finished growing. As the brain continues to grow, it pushes on the skull from the inside but cannot expand into the closed over area. This causes the skull to have an unusual shape.

Take your baby to see their doctor or paediatrician if:

• you think that your baby's fontanelles seem to have closed early
• you can feel a ridge along your baby's skull
• you think that your baby's head has an unusual shape

Your baby's fontanelles may not close on time for several reasons.

Common reasons for delayed fontanelle closure include:

• congenital hypothyroidism (low levels of thyroid hormones)
• Down syndrome
• increased pressure inside the brain
• rickets
• familial macrocephaly (a genetic tendency to have a large head)

If you have any concerns about your baby's fontanelles, see your doctor, child health nurse or paediatrician.

If one or both of your baby's fontanelles haves not closed by the time they are 2 years old, speak to your doctor or paediatrician.

The Pregnancy, Birth and Baby video call service allows you to speak face-to-face with a maternal child health nurse. Video call is a free service and is available from 7am to midnight (AET), 7 days a week (including public holidays).