Perinatal & Pediatric
Characterizing postnatal trajectories of breast bud diameter in male and female infants using latent class mixed models Paige E. Tomer* Paige Tomer Shanshan Zhao Natalie D. Shaw Virginia A. Stallings Andrea Kelly Walter J. Rogan David M. Umbach Mandy Goldberg
Background: Most infants are born with breast tissue that is expected to regress. The natural history of breast tissue across minipuberty, a period of sex-specific postnatal endocrine activity, has not been well-characterized. Our objective was to describe variation in sex-specific age trajectories of breast bud diameter across minipuberty.
Methods: We used data from 147 boys and 136 girls participating in the Infant Feeding and Early Development study, a longitudinal cohort of healthy, term infants enrolled during 2010-2013 from the Philadelphia area. Breast bud diameter was assessed via ultrasound within 72 hours of birth and every 4-8 weeks thereafter up to 24 weeks in boys and 32 weeks in girls. We log2-transformed the geometric mean of left and right breast bud diameters and applied latent class linear mixed models to cluster age trajectories of breast bud diameter in boys and girls separately. We selected the number of latent classes using several statistical metrics and visual inspection. We used the LCMM package in R 4.4.1 for model fitting.
Results: We identified two trajectory groups in boys: one with a larger diameter at birth that declined with age (n=115, 78%), the other with a smaller initial diameter that remained stable (n=32, 22%); the groups converged by age 24 weeks (Figure 1a). Three trajectory groups were identified in girls: stable (n=75, 55%), decreasing (n=42, 31%), and increasing (n=19, 14%) (Figure 1b). Compared to the stable group, the decreasing group had a similar diameter at birth that decreased with age, whereas the increasing group started with a smaller diameter and converged with the stable group by age 20 weeks.
Conclusions: We identified distinct patterns of breast bud diameter in male and female infants; patterns that may reflect differences in endocrine activity during minipuberty. Most infant girls maintained or experienced growth in breast bud tissue, while only a minority exhibited the expected regression by 32 weeks of age.
