Body fat in neonates and young infants: validation of skinfold thickness versus dual-energy X-ray absorptiometry.

BACKGROUND There is an interest in noninvasive measurement of body fat in newborns and infants. Measurement of skinfold thickness (SFT) is a simple clinical method. OBJECTIVE We correlated fat mass (FM) values of neonates and infants predicted from SFT measurements and compared them with FM values measured by dual-energy X-ray absorptiometry (DXA), a validated in vivo method for determining body fat. DESIGN The weight, length, body composition (DXA measurement of FM and percentage of body fat), and SFT of 104 healthy term and preterm infants were measured at 0, 2, and 4 mo of age. RESULTS Mean (+/- SD) FM determined by DXA increased from 440 +/- 220 g at birth to 1310 +/- 450 g at 2 mo of age and to 2170 +/- 605 g at 4 mo of age. The percentage of body fat increased from 13.3% at birth to 24.5% and 31.2% at 2 and 4 mo of age, respectively. An equation was developed to calculate FM (in g) in newborns by using the sum of SFT measurements (in mm) and body length (l; in cm): FM = 68.2 x SigmaSFT((0.0162) x l) - 172.8 (R(2) = 0.948, P < 0.001). CONCLUSIONS With the use of statistical bootstrap analysis, the results provide an in vivo validation of SFT measurements against DXA for newborns and young infants. Body fat measurements by SFT correlate with FM values determined by DXA (R(2) = 0.936). Estimation of nutritional status is possible with errors (SD) of +/- 75, +/- 170, +/- 300, and +/- 380 g for infants with an FM 2000 g, respectively.