The baby’s soft spot, medically known as a fontanelle, consists of spaces between the bony plates of the skull that have not yet fused together. These spots are covered by a thick, durable membrane, making them far more resilient than they might seem. Understanding this area is a common part of caring for a newborn, and it serves several important biological purposes.
Pinpointing the Soft Spots: Anatomy and Location
A newborn has several fontanelles, but two are primary. The largest and most commonly recognized is the anterior fontanelle, located on the top of the head toward the front. This space has a distinct diamond shape and is situated where the two frontal bones meet the two parietal bones of the skull. At birth, the anterior fontanelle typically measures between one and three centimeters across.
The second primary soft spot is the posterior fontanelle, which is much smaller and found at the back of the head. This fontanelle is triangular in shape and is positioned where the two parietal bones meet the occipital bone. The posterior fontanelle is usually less than half a centimeter in diameter at birth. These unossified areas are made of strong, fibrous connective tissue that provides flexibility to the infant’s cranium.
Essential Functions During Birth and Growth
The primary reason these soft spots exist is for the process of childbirth. The unfused skull plates allow the head to be temporarily compressed and molded during passage through the narrow birth canal. This process, known as molding, involves the skull bones overlapping slightly, reducing the head’s diameter to facilitate a smoother delivery. Without this flexibility, the risk of injury to both mother and baby would be higher.
Beyond labor, the fontanelles accommodate the rapid growth of the infant brain, particularly during the first year of life. These flexible spaces provide the necessary room for the brain to grow without being constricted by a rigid skull. This feature ensures the developing brain has the space it needs to mature.
The Developmental Timeline for Fontanelle Closure
The closure of the fontanelles occurs when the fibrous tissue is gradually replaced by bone. The smaller posterior fontanelle is the first to close, typically fusing after birth. This closure commonly occurs within the first one to three months of the baby’s life.
The larger anterior fontanelle remains open for a longer period to accommodate continued brain growth. Complete closure is generally expected between 7 and 18 months of age. The exact timing can vary widely among healthy infants, but pediatricians monitor this timeline closely during well-baby visits.
Recognizing Normal Appearance and Warning Signs
When a baby is calm and upright, a normal fontanelle should feel flat or exhibit a slight, inward curve when gently touched. It is normal to observe a slight rhythmic pulsing of the soft spot. This movement is the blood flowing through the vessels and corresponds directly with the baby’s heartbeat. Parents should not fear gently touching or washing the area, as the protective membrane is resilient enough for routine care.
A significant change in the soft spot’s appearance can indicate an underlying health issue. A sunken or depressed fontanelle is a sign of dehydration. This appearance is often accompanied by other symptoms, such as a decrease in wet diapers, dry lips, or lethargy, and requires prompt medical evaluation.
A bulging or tense fontanelle that remains prominent when the baby is calm and upright is also a cause for concern. While the soft spot may temporarily bulge during crying, coughing, or vomiting, a persistent bulge signals increased pressure inside the skull. This can be a sign of a serious condition, such as infection or fluid buildup. If a bulging fontanelle is noted along with a fever, excessive sleepiness, or persistent vomiting, a pediatrician should be contacted immediately.