Presented at the Neonatal Society 2013 Autumn Meeting.
Gale C, Jeffries S, Parkinson JRC, Santhakumaran S, Durighe G, Uthaya S, Thomas EL, Bell JD, Modi N
Imperial College London, UK
Background: Sexual dimorphism in adipose tissue distribution and ectopic lipid are well described in adults and adolescents, but the point in childhood when differences in adiposity begin to manifest is unknown. We aimed to describe the longitudinal changes in directly measured adiposity and hepatic lipid that occur in early infancy, in healthy term babies and in relation to infant sex.
Methods: Research Ethics Committee and NHS approvals were obtained. With informed maternal consent, healthy, term infants underwent whole body magnetic resonance imaging and hepatic spectroscopy to assess body composition and intrahepatocellular lipid (IHCL) content. Investigations were performed in natural sleep on two occasions, shortly after birth (T1), and between two and three months (T2) in accordance with our previously published protocols (1, 2). Anthropometric measurements were obtained at both visits. Total adipose tissue volume was calculated as the sum of six individually quantified adipose tissue compartments (superficial subcutaneous abdominal (SSCA), superficial subcutaneous non-abdominal (SSCNA), deep subcutaneous abdominal DSCA), deep subcutaneous non-abdominal (DSCNA), internal abdominal (IA), and internal non-abdominal (INA)). We used multivariable regression to examine total and regional adipose tissue volumes in relation to sex, with adjustment for body weight at scan. Mean differences in adipose tissue volumes (litres) between male and female infants are presented as mean (95% confidence interval). IHCL is non-normally distributed therefore logetransform was taken.
Results: Sixty-nine infants (39 male), mean (SD) birthweight 3.402kg (0.400), gestational age 40+0 (1+2) and maternal BMI 23.5 (3.9), underwent longitudinal scans at a median [interquartile range] age of 13 [7-19] days at T1 and 63 [56-70] days at T2. No significant differences were detected in anthropometric measures at birth, T1 or T2 between male and female infants. Data for mean differences in adiposity (litres), male infants compared to female infants and after adjustment for weight, are presented in table 1. No significant difference in IHCL was detected between male and female infants at T1 or T2.
Table 1: Mean differences (95% confidence intervals) between male and female infants
Conclusion: Female infants are more adipose than male infants in the neonatal period and this difference becomes more pronounced in early infancy. The greater relative adiposity that characterises female infants is explained by more subcutaneous adipose tissue; no significant differences are seen in internal abdominal adipose tissue or in IHCL. Sex specific differences in subcutaneous adipose tissue are in keeping with those described in later life and suggest that sexual dimorphism in adiposity is, at least in part, established in the perinatal and infant period. The absence of detectable differences in internal abdominal adipose tissue and IHCL is in contrast to the pattern observed in adults, suggesting that alternate mediators of these lipid stores may operate in early life.
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1. Modi N, Murgasova D, Ruager-Martin R, Thomas EL, Hyde MJ, Gale C, et al. The influence of maternal body mass index on infant adiposity and hepatic lipid content. Pediatr Res. 2011;70(3):287-91.
2. Uthaya S, Bell J, Modi N. Adipose tissue magnetic resonance imaging in the newborn. Horm Res. 2004;62 Suppl 3:143-8.