<p>Summary of background characteristics. (a) all infants, (b) infants with glabella-occipital protuberance (G-O), left tragion-right tragion (LT-RT), and head circumference (HC) measurements, excluding age groups other than 2, 3, 6, and 12 months, (c) the number of infants with G-O, LT-RT, and HC data in each age group and (d) the number of 3-month-old infants with G-O, LT-RT, HC data in each birth year group.</p>

Summary of background characteristics. (a) all infants, (b) infants with glabella-occipital protuberance (G-O), left tragion-right tragion (LT-RT), and head circumference (HC) measurements, excluding age groups other than 2, 3, 6, and 12 months, (c) the number of infants with G-O, LT-RT, and HC data in each age group and (d) the number of 3-month-old infants with G-O, LT-RT, HC data in each birth year group.