Relationship Between Birthweight for Gestational Age and Colostrum Macronutrient Composition: A Comparative Analysis in Small, Appropriate, and Large for Gestational Age Infants.

Background: Human milk and colostrum have been well studied; however, limited data are available on the variations in macronutrient content when compared across different infant weight categories for infants with similar gestational ages.

Research aims: To compare the colostrum macronutrient content of participants who delivered term infants classified as small for gestational age, appropriate for gestational age, and large for gestational age.

Methods: In this exploratory cross-sectional observational study (N = 252), colostrum (on postpartum Day 2) was collected and categorized by gestational weight group. The protein, fat, carbohydrate, and energy levels of colostrum were measured using a mid-infrared human milk analyzer. Values were dichotomized at the median and compared using logistic regression.

Results: Median colostrum protein content was significantly higher in the small for gestational age (4.8 [IQR = 3-6.4] gr/dl) and large for gestational age (4.4 [IQR = 3.5-5.3] g/dl) groups compared to the appropriate for gestational age group (2.8 [IQR = 2.1-3.7] g/dl; p < 0.001). Median carbohydrate content was significantly higher in the large for gestational age group (5.3 [IQR = 4.2-6] g/dl) than appropriate for gestational age group (4.5 [IQR = 3.5-5.3] g/dl; p = 0.002). In multivariate analysis, being SGA or LGA was independently associated with higher milk protein content (OR 4.68; 95% CI [2.25, 9.77; p < 0.001; and OR 6.76; 95% CI [3.30, 13.87]; p < 0.001, respectively). Only being LGA was associated with higher carbohydrate content (OR 2.74; 95% CI [1.46, 5.16]; p = 0.002).

Conclusion: Colostrum macronutrient content varies depending on whether the birthweight is small or large for gestational age. Studies are needed to investigate these potential associations and the clinical consequences of this relationship.