Reduced calf muscle growth in NICU graduates compared with typically developing term infants: 12-month longitudinal study of infant muscle growth.

Abstract

Objective: To evaluate growth of the triceps surae muscle over the first 12 months of life in neonatal intensive care unit (NICU) graduates compared with typically developing (TD) infants.

Design: Longitudinal, prospective study.

Participants: Sixty-one infants, n=24 TD (15 male) and n=37 NICU graduates designated as intermediate-risk (NICU-IR; n=14, 9 male) or higher-risk (NICU-HR; n=23, 11 male) based on additional risk factors (including <28 weeks gestational age; <1000 g; neonatal encephalopathy; abnormal neuroimaging; small for gestational age).

Outcome measures: Sequential assessments at corrected ages 3, 6 and 12 months of muscle volume (freehand three-dimensional ultrasound) and gross motor development (Peabody Developmental Motor Scale-2, Gross Motor Quotient (GMQ)). Linear mixed models analysed muscle volume trajectories.

Results: Triceps surae growth trajectories differed significantly by group (p<0.001). Between 3 and 12 months, triceps surae increased on average by 18.1 cm³ (95% CI 16.1 to 20.2 cm³), 13.3 cm³ (10.6 to 16.0 cm³) and 12.5 cm³ (10.5 to 14.6 cm³) in TD, NICU-IR and NICU-HR infants, respectively. Soleus was significantly smaller at 6 and 12 months for both NICU groups, and lateral gastrocnemius was smaller at 12 months for NICU-HR (p<0.001). At 12 months of age, 8% of NICU infants and 30% of the TD infants were walking, the GMQ was >90 in all TD infants, and all but 5 (14%) NICU infants. Muscle volumes at 12 months were positively associated with both gestational age and birth weight.

Conclusion: Reduced soleus growth from 3 to 12 months led to a 25% smaller triceps surae muscle at 12 months in NICU graduates.