Medicine · 3 authors, 2 centres
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This study measured anterior fontanel (AF) sizes in 573 Korean nursery newborns, finding a mean AF size of 1.85 ± 0.83 cm — the smallest reported among various ethnic groups. Small for gestational age (SGA) weight and head circumference were significant risk factors for large AF size. Among 18 infants with large AF (>3.6 cm), 2 had intracranial abnormalities and 11 of 16 tested had vitamin D deficiency, suggesting that large AF warrants clinical evaluation for underlying pathology.
**Background:** The anterior fontanel (AF) is the largest fontanel in the newborn skull, and its size can provide clues about cranial growth, ossification, and underlying pathology. While AF size varies by ethnicity and geographic region, no published data existed for Korean newborns. Abnormally large AF may be associated with increased intracranial pressure, skeletal anomalies, chromosomal abnormalities, hypothyroidism, and intrauterine malnutrition, but the cutoff for large AF and its etiologies are not well established.
**Methods:** This retrospective cohort study included 573 nursery newborns born at Kangwon National University Hospital, Chuncheon, South Korea, from September 2019 to August 2020. Inclusion criteria were gestational age (GA) ≥36 weeks and birth weight >2000 g. Exclusions included NICU admission, obvious dysmorphism, head birth injuries (cephalhematoma, caput succedaneum, severe molding, sub-galeal bleeding), and infants of foreign parents. AF size was measured at 24–48 hours after birth by 3 attending physicians using a non-stretch plastic measuring tape, calculated as (anterior-to-posterior length + right-to-left width)/2. A large AF was defined as >3.6 cm based on prior literature. Infants with large AF underwent brain ultrasonography, thyroid function tests, and serum calcium/vitamin D assessment. Growth percentiles were calculated using Fenton growth charts; SGA was defined as below the 10th percentile. Statistical analyses included Pearson correlation, Kruskal–Wallis test, Mann–Whitney U test, and Fisher exact test, with significance set at P < .05.
**Key Results:** The mean GA was 38.5 ± 1.2 weeks (range 36+0–41+2 weeks) and mean birth weight was 3140 ± 450 g (range 2000–4500 g). The mean AF size was 1.85 ± 0.83 cm (range 0.30–5.35 cm). The 90th and 97th percentiles were 2.96 cm and 3.65 cm, respectively. AF size was not correlated with GA, birth weight, delivery mode, or gender. SGA weight (P = .034, R = 0.089), SGA head circumference (P < .001, R = 0.142), twin births (P = .016, R = 0.101), and craniotabes (P < .001, R = 0.176) were significantly correlated with larger AF size. Among 18 infants with large AF (>3.6 cm), none had bone abnormalities or thyroid dysfunction. Two had intracranial abnormalities on brain ultrasonography (1 epidural hematoma, 1 communicating hydrocephalus). Among the remaining 16 infants, mean serum 25-hydroxyvitamin D level was 19.6 ± 5.3 ng/mL; 11 (69%) had vitamin D deficiency (<20 ng/mL) and 5 (31%) had insufficiency (20–29 ng/mL). Two infants had craniotabes with vitamin D deficiency. In the large AF group, 5 of 16 (31.3%) had SGA weight and 4 of 16 (25%) had SGA head circumference. Compared to others in the cohort, the large AF group had significantly more twins (22.2% vs. 8.6%, P = .049), SGA weight (27.8% vs. 9.9%, P = .015), SGA head circumference (22.2% vs. 8.3%, P = .039), and craniotabes (11.1% vs. 0.5%, P = .001).
**Clinical Implications:** This is the first recent study of AF size in Korean newborns, reporting a mean AF size of 1.85 ± 0.83 cm — the smallest mean AF size reported among various ethnic groups globally. The 97th percentile cutoff of 3.65 cm aligns with the clinically used threshold of 3.6 cm. SGA weight and SGA head circumference are significant risk factors for large AF, likely reflecting delayed intrauterine osseous maturation due to nutritional deprivation. The finding that 69% of large AF infants had vitamin D deficiency (vs. reported rates in the general Korean newborn population) suggests that vitamin D deficiency may be a frequent underlying etiology. Clinically, large AF in newborns warrants evaluation for intracranial pathology (found in 2 of 18 infants) and vitamin D status. Limitations include single-center design, lack of maternal nutritional assessment, and absence of vitamin D levels in the comparison group. Future multicenter studies with universal vitamin D screening (e.g., cord blood) are needed to confirm the association between vitamin D deficiency and AF size.