Determinants of Infant Growth within the First Six Months of Life
Authors: Burklin Aubrey , Wilson Kelsey , Lovelady Cheryl 
Published: November 2023

Infants who gain weight rapidly during the first year of life are more likely to be overweight later in childhood. Suggested predictors of infant weight gain are: prepregnancy BMI, gestational weight gain (GWG), infant birth weight, and formula feeding. Recently, feeding human milk from a bottle has been suggested to contribute to rapid weight gain. When feeding at the breast, the pace and volume of intake are controlled by the infant. Shifting feeding control from infant to mother may affect the infant's ability to interpret satiety cues. Infants fed from a bottle, compared to those fed directly at the breast, may consume more milk. This greater consumption of milk could potentially result in greater subsequent weight gain over time. Therefore, the objective of this study was to determine if mode of feeding human milk was related to infant growth in the first six months of life, controlling for prepregnancy BMI, GWG, and birth weight. Weight, length, and triceps and subscapular skinfolds were measured at 2, 4, and 6 months. Mothers reported birth weight and length and completed monthly questionnaires on infant feeding practices (e.g., number of human milk feedings by bottle or breast per day, age of introduction to complementary foods, and infant bottle‐emptying behavior). Infants were divided into 2 groups based on their breastfeeding intensity across the first 6 months of life: Nursing Group (NG, n=34): infants fed human milk with more than 80% of the feeds fed directly at the breast and Bottle Group (BG, n=16): infants fed human milk from the bottle with less than 80% of the feeds fed directly at the breast. There was a significant difference between the groups average breastfeeding intensity from birth to 6 months (NG=91.1 ± 7.2%, BG= 64.8 ± 14.4%, P<0.001). There were no significant differences between groups in maternal age (NG= 30.5 ± 4.2 BG=29.6 ± 3.1), income, education level, prepregnancy BMI (kg/m2) (NG= 24.9 ± 3.8, BG= 24.0 ± 3.3), GWG (kg) (NG= 17.6 ± 5.6, BG= 15.8 ± 4.2), and birth weight (kg) (NG= 3.70 ± 0.5, BG=3.62 ± 0.5). Infants fed human milk from the bottle finished the bottle “most or all of the time,” with a bottle size of 3 to 4 ounces at each feed. No infants were introduced to complementary foods before 4 months. There were no significant differences in triceps and subscapular skinfolds between groups at 2, 4, and 6 months. There was no significant difference between groups in change in weight for length Z score (WLZ) from birth to six months (NG=1.43 ± 1.85, BG=2.29 ± 2.04, P= 0.14). However, in multivariate regression analysis, prepregnancy BMI (β = 0.086), birth weight (β = 0.938), WLZ at birth (β = ‐0.927) and breastfeeding at a lower intensity (β = 0.861) significantly predicted change in WLZ from birth to 6 months (R2 = 0.61, P < 0.001). There was not a significant difference between groups in weight gain velocity percentiles from birth to 6 months (NG=0.45 ± 0.29, BG=0.53 ± 0.29, P= 0.35). Birth weight (β = −0.129), prepregnancy BMI (β = 0.035), and breastfeeding at a lower intensity (β = 0.108) significantly predicted weight gain velocity from birth to 6 months (R2 = 0.17, P < 0.02). These results suggest that among infants not receiving formula or complementary foods before four months, feeding human milk from the bottle more than 20% of the time may contribute to increased weight for length gain from birth to 6 months.