How Many Fontanelles Does a Newborn Have, and Where Exactly Are They?

A newborn has six fontanelles (“soft spots” on the skull): 1 anterior (front), 1 posterior (back), 2 sphenoidal/sphenoid (front sides) and 2 mastoid (back sides). Their role is to allow the baby’s head to pass through the birth canal and to accommodate rapid brain growth in the first months of life. Normally they are flat and firm to the touch, and you may sometimes feel a gentle pulsation (normal). Closure: the posterior usually by 6–8 weeks, the sphenoidal around 6 months, the mastoid roughly 6–18 months, and the anterior most commonly 13–24 months. (NCBI)

Where exactly are the fontanelles and what borders them

• Anterior – at the crown of the head, diamond-shaped, between the frontal and parietal bones; the coronal and sagittal sutures meet here.
• Posterior – smaller, triangular, at the junction of the parietal bones and the occipital bone; at the lambdoid suture.
• Sphenoidal (anterolateral, paired) – on the front sides near the temples; junction of the frontal, temporal, parietal, and sphenoid bones.
• Mastoid (posterolateral, paired) – on the back sides behind the ear; junction of the temporal, parietal, and occipital bones.
  These areas are membranous connective-tissue bridges between the flat skull bones—“zippers” that later turn into firm sutures. (NCBI)

Why they exist at all, and what develops “underneath”

Beneath the fontanelles, the brain develops rapidly and the cranial vault grows as well. After birth, the skull bones strengthen through intramembranous ossification: osteoblasts add layers of bone from the outside, while other cells on the inside remove excess—resulting in the gradual “closure” of the soft spots. That is why fontanelles are temporary windows of growth; through the anterior fontanelle you can sometimes feel physiologic pulsation from blood flow—this is not a sign of disease. (NCBI)

When fontanelles typically close

• Posterior: usually 6–8 weeks after birth.
• Sphenoidal (both): around 6 months.
• Mastoid (both): roughly 6–18 months.
• Anterior: most often 13–24 months (normal variation is wide).
  Individual differences are normal—your pediatrician considers the overall development, head circumference, and the full clinical picture, not just a “closure date.” (NCBI)

What a normal fontanelle looks like—and what is a warning sign?

• Normal: the skin is intact; the area is flat to slightly sunken, firm to the touch, and may gently pulsate.
• Temporarily full/bulging when crying or lying down: can be physiologic (it’s assessed when the baby is calm and upright). (NCBI)
• Markedly sunken + dry diapers, poor fluid intake → may suggest dehydration—contact a doctor. (HealthyChildren.org)
• Markedly bulging at rest (not due to crying, vomiting, or position) + other symptoms (fever, sleepiness, vomiting) → urgent evaluation for possible increased intracranial pressure (e.g., infection, bleeding, hydrocephalus). (Merck Manuals)

How and why the pediatrician monitors them

At each well-child visit, the pediatrician examines the head: checks the head shape, palpates sutures and fontanelles, measures head circumference, and plots the result on growth percentile charts. They also look for conditions associated with abnormalities—for example, a large anterior fontanelle or an unusually open posterior fontanelle, which can accompany certain endocrine or genetic diagnoses (e.g., hypothyroidism). (Merck Manuals)

Myths and facts: Can I touch the fontanelle?

Yes. Fontanelles are covered by a tough layer of connective tissue, so gentle touching, washing, or brushing your baby’s hair won’t harm them. More important is changing your baby’s head position (when sleeping on the back, alternate left and right) and ensuring tummy time while awake to help prevent flattening in one area. (nhs.uk)

Rare: a “third” fontanelle

Rarely, an additional small soft spot is described along the midline between the anterior and posterior fontanelles. Most often it is a normal variant, but it is more commonly associated with Down syndrome or some congenital infections—your doctor assesses this in the context of the overall findings. (NCBI)

Practical tips for monitoring at home

• Hydration: number of wet diapers, behavior, temperature. If you’re unsure, call your pediatrician sooner rather than later.
• Positioning: alternate which side your baby turns their head to in the stroller and crib; do regular tummy time while awake.
• Checkups: don’t skip routine well-child visits—this is where it’s often caught early whether the head and fontanelles are progressing as they should.
• When to seek care: a fontanelle that stays bulging at rest, a noticeably sunken fontanelle with signs of dehydration, forceful vomiting, fever, lethargy, or seizures.

Video: what a newborn head exam looks like

A short professional demonstration from OPENPediatrics (section Head/Fontanelles):

Sources

1. StatPearls – Anatomy, Head and Neck: Fontanelles. https://www.ncbi.nlm.nih.gov/books/NBK542197/
2. NHS – Your newborn baby (Fontanelles section). https://www.nhs.uk/pregnancy/labour-and-birth/after-the-birth/getting-to-know-your-newborn/
3. HealthyChildren.org (AAP) – Your Baby’s Head. https://www.healthychildren.org/English/ages-stages/baby/Pages/Your-Babys-Head.aspx
4. Merck Manual Professional – Physical Examination of the Newborn.https://www.merckmanuals.com/professional/pediatrics/care-of-newborns-and-infants/physical-examination-of-the-newborn