Normal Range of Anterior Fontanelle Size in Newborns
An anterior fontanelle size of 1 cm × 1 cm in a newborn baby is within the normal range, though at the smaller end of the spectrum.
Normal Fontanelle Size Parameters
- The average size of the anterior fontanelle in neonates ranges from 0.3 to 2.5 cm, with a mean value of approximately 1.5 cm 1
- A study of term neonates found that the anterior fontanelle size ranged from 1.0 to 6.4 cm with a mean of 4.0 cm 2
- Another study reported anterior fontanelle sizes ranging from 1.7 to 5.5 cm with a mean of 3.0 cm in term neonates 3
- In full-term infants, the width (50th percentile) at birth is approximately 2.0 cm 4
Factors Affecting Fontanelle Size
- Gender differences exist, with male neonates typically having larger anterior fontanelles (mean 3.10 cm) compared to females (mean 2.88 cm) 3
- The size of the anterior fontanelle is not significantly correlated with the development levels of weight, length, and head circumference in most studies 1
- However, some research has found a significant positive correlation between anterior fontanelle size and both birth weight and head circumference 3
- Mode of delivery and duration of labor can affect fontanelle size 3
Clinical Significance of Fontanelle Size
- The anterior fontanelle is the largest and most important fontanelle for clinical evaluation 5
- A fontanelle that is abnormally large or shows delayed closure may indicate conditions such as achondroplasia, hypothyroidism, Down syndrome, increased intracranial pressure, or rickets 5
- A bulging anterior fontanelle can result from increased intracranial pressure or intracranial and extracranial tumors 5
- A sunken fontanelle usually indicates dehydration 5
Normal Fontanelle Development
- The anterior fontanelle typically reaches its maximum size (mean 2.2 cm) at approximately 1 month of age 1
- After reaching its maximum size, the fontanelle gradually decreases in size over time 1
- By 12 months of age, the average size decreases to approximately 1.0 cm 1
- Complete closure occurs in approximately 26.5% of infants by 12 months and 93% by 24 months 1
Evaluation Techniques
- Physical examination remains the primary method for assessing fontanelle size 5
- Ultrasonography through the fontanelle provides an excellent window to examine the infant brain without radiation exposure 6
- Transfontanellar ultrasound can be used to evaluate newborns or young infants with open fontanelles for various intracranial conditions 6
Clinical Implications of a 1 cm × 1 cm Fontanelle
- A fontanelle size of 1 cm × 1 cm falls within the lower end of the normal range for newborns 1, 4
- While this size is smaller than some reported averages, it still falls within normal parameters and is not necessarily indicative of a pathological condition 1, 4, 2
- Regular monitoring of fontanelle size and closure is recommended as part of routine pediatric care 5