IGF-I, Growth, and Body Composition in Preterm Infants up to Term Equivalent Age

Abstract

Context: There are concerns that a higher fat mass in the early life of preterm infants is associated with adverse cardiometabolic outcomes in young adulthood.

Objective: To investigate the role of IGF-I and growth in determining body composition of preterm infants at term equivalent age.

Methods: An observational study was conducted from August 2015 to August 2018. From birth to term equivalent age, IGF-I levels were measured bi-weekly and growth was assessed weekly. At term equivalent age, body composition was assessed through air displacement plethysmography; 65 infants with a gestational age of 24 to 32 weeks were assessed at term equivalent age, of whom 58 completed body composition measurement. The main outcome measures were fat (free) mass (g) and fat (free) mass percentage at term equivalent age.

Results: In the first month of life, each 0.1 nmol/L per week increase in IGF-I was associated with a 465 g (SE 125 g) increase in fat free mass. A greater increase in weight SDS in the first month of life was associated with a higher fat free mass percentage (B 200.9; 95% CI, 12.1-389.6). A higher head circumference SDS was associated with more fat free mass (r = 0.46; 95% CI, 0.21-0.65). However, a greater increase in weight SDS up to term equivalent age was associated with a lower fat free mass percentage (B -55.7, SE 9.4).

Conclusion: These findings suggest that impaired growth in the first month of life is associated with a less favorable body composition at term equivalent age.

Keywords: IGF-I; body composition; growth; preterm infants.

Figure 1.

Enrollment and follow-up of study participants.

Figure 2.

Postnatal growth and IGF-I levels in preterm infants. A, Mean weight z-scores (Fenton 2013) up to term equivalent age. B, Mean length z-scores (Fenton 2013) up to term equivalent age. C, Mean head circumference z-scores (Fenton 2013) up to term equivalent age. D, Mean IGF-I levels up to term equivalent age. Umbilical cord blood samples were excluded from this graph. Abbreviations: PMA, postmenstrual age.

Figure 3.

Weight gain in relation to IGF-I and body composition in preterm infants. A, Change in IGF-I in relation to change in weight SDS up to 36 weeks PMA (r = 0.62 [95% CI, 0.46-0.74; P < 0.001]). B, Change in weight SDS from 30 weeks PMA onwards in relation to fat free mass and fat mass at term equivalent age. Partial correlation with fat free mass (r = 0.72 [95% CI, 0.56-0.82; P < 0.001]); partial correlation with fat mass (r = 0.77 [95% CI, 0.65-0.86; P < 0.001]) Correlations were controlled for gestational age at birth and postmenstrual age at time of body composition measurement. C, Change in weight SDS from 30 weeks PMA onwards in relation to fat free mass percentage at term equivalent age. Linear regression model: R²: 0.45 P < 0.001, B for change in weight SDS −54.0 (95% CI, −72.0 to −35.9, P < 0.001) (gestational age at birth and postmenstrual age at the time of body composition measurement were entered in the regression model as covariates). Abbreviations: PMA, postmenstrual age.