316 - Ultrasound measurements of quadriceps cross-sectional area are not predictive of preterm infant fat-free mass z-scores at discharge from the neonatal intensive care unit

Poster Number: 316
Publication Number: 316.129

Emily Nagel, University of Minnesota School of Public Health, St Paul, MN, United States; Marie Hickey, University of Minnesota Masonic Children's Hospital, Minneapolis, MN, United States; Tara Holm, University of Minnesota Masonic Children's Hospital, Minneapolis, MN, United States; Ellen W. Demerath, University of Minnesota, Minneapolis, MN, United States; Sara E. Ramel, University of Minnesota Masonic Children's Hospital, North Oaks, MN, United States

Background: Previously, we found that greater fat-free mass (FFM) was associated with improved neurodevelopmental outcomes for preterm infants in later infancy. However, many body composition tools that can be used to assess FFM in preterm infants are invasive or expensive and have limited utility in the clinical setting. Bedside ultrasound is non-invasive and can be conducted in critically ill and healthy infants, making it ideal for longitudinal measurements in the inpatient setting. 

Objective: We aimed to determine the ability of ultrasound measures of quadriceps cross-sectional area (CSA) to predict FFM z-scores obtained at discharge from the neonatal intensive care unit (NICU).

Design/Methods: Forty-eight preterm infants had ultrasound images where the rectus femoris was readily visualized. Infant whole body FFM was obtained using air displacement plethysmography on the same day ultrasound measurements were taken. Crude and adjusted linear regression analyses tested associations between rectus femoris cross-sectional area (CSA) and FFM z-scores. Models were adjusted for infant gestational age at birth, sex, and age, weight, and length at the study visit.

Results:

Infants were born at a mean gestational age of 31.5 ± 2.44 weeks, measured at a mean age of 35.5 ± 1.45 weeks, and had a mean FFM z-score of -0.15 ± 1.39. Mean quadriceps cross-sectional area was 0.31 cm² ± 0.12. In the crude model, quadriceps CSA was significantly associated with FFM z-score (β = 4.39 ± 1.61, p =.01, R²=0.14). In the adjusted model (R² = 0.88, RMSE = 0.52), CSA was not significantly adjusted with FFM z-score (β = 0.95 ± 0.75, p =0.21), while infant weight (β = 3.95 ± 0.46, p < .0001), age at study visit (β = -0.82 ± 0.09, p < .0001), and sex (β = -0.52 ± 0.17, p =0.005) were significantly associated with FFM z-score.

Conclusion(s):

In this cohort of preterm infants, ultrasound measurements of quadriceps CSA were not predictive of preterm infant FFM z-scores at discharge. Further work is needed to determine prediction equations which can accurately estimate fat-free mass and adiposity in preterm infants.