Will the anterior fontanelle of a 2-month-old baby, which is currently smaller than average, enlarge later?
May 25, 2022
Source: Cainiu Health
Dr. Xie Zixing
Introduction
In a 2-month-old infant, a relatively small anterior fontanelle may subsequently increase in size. The fontanelle refers to the cranial gaps formed due to incomplete ossification and fusion of the skull bones in infants and young children; typically, this term denotes the anterior fontanelle. Located at the top of the head, the anterior fontanelle is a diamond-shaped gap formed by the sutures between the two frontal bones and the two parietal bones. It is precisely this gap that accounts for the observed variability—sometimes larger, sometimes smaller—in the fontanelle’s size.
In a 2-month-old infant, a relatively small anterior fontanelle may subsequently increase in size. The fontanelle refers to the cranial gaps formed due to incomplete ossification and fusion of the skull bones in infants and young children—most commonly referring to the anterior fontanelle. Located at the top of the head, the anterior fontanelle is a diamond-shaped gap formed by the sutures between the two frontal bones and the two parietal bones. It is precisely this gap that allows the fontanelle’s size to fluctuate—appearing alternately larger or smaller.
Prior to 6 months of age, an infant’s fontanelle size remains variable, influenced by factors such as birth-related conditions and sleeping position. Normally, the posterior fontanelle is very small—or already closed—at birth, measuring approximately the size of a fingertip; it typically closes completely by 6–8 weeks after birth. At birth, the anterior fontanelle measures about 1.5–2.5 cm in diagonal diameter. Following birth, as the head develops and head circumference gradually increases, the anterior fontanelle may also enlarge. After 6 months, however, progressive ossification of the cranial bones causes the anterior fontanelle to gradually decrease in size, usually closing completely between 12 and 18 months of age.
In rare cases, prenatal maternal infection or other pathological conditions impair fetal brain development, resulting in microcephaly (abnormally small head size) and a correspondingly small head circumference at birth. In such instances, the anterior fontanelle may close prematurely—within 5–6 months after birth—leading to microcephaly. Conversely, some infants aged 5–6 months may exhibit an anterior fontanelle reduced to only fingertip size, giving the impression of imminent closure; however, if ossification has not yet occurred, this does not constitute premature closure. As long as head circumference remains within normal limits—i.e., ≥46 cm at 1 year of age and ≥47–48 cm at 2 years—the infant is considered healthy, and no concern is warranted.
