Effect of Thickening on Flow Rates Through Bottle Nipples

Objective: To compare the flow rates of formula of various thicknesses through bottle nipples.

Design: Multiple crossover design.

Setting: Laboratory experiment.

Participants: No human subjects.

Methods: We used established methods to test the flow rates of UltraPreemie; Preemie; Newborn; and Levels 1, 2, 3, and 4 nipples with three thicknesses of formula: thin, slightly thick, and mildly thick. We used descriptive statistics to calculate mean flow rates (milliliters per minute) and standard deviation, from which we calculated the coefficient of variation. We used cluster analysis to identify nipple types and thicknesses with comparable flow rates.

Results: Flow rates ranged from less than 1 ml/min for the Preemie nipple with mildly thick formula to 82.29 ml/min for the Level 4 nipple with thin formula. As expected, within each nipple type, increased thickness of formula resulted in decreased flow. Increased thickness of formula also resulted in an increased variability in flow rate. For nearly all nipple types, mildly thick consistency resulted in the greatest amount of variability in flow. We identified seven clusters of nipple types and formula thicknesses with comparable flow rates.

Conclusion: These data provide clinicians with information to guide decision making about nipple choice when thickened feedings are needed. Thickening increases the variability in flow rates, which is an important consideration for infants who are still learning to safely and effectively feed by mouth.