Are Infants Doubling Their Birth Weight Sooner?

Background: In general, pediatric birth weight doubles at 5 to 6 months of age in the first year. Doubling of birth weight at an earlier age has been observed, as this has been an anecdotal observation, we aim to more accurately evaluate the cause. We conducted this study to determine the age at which birth weight doubles in the population of South Bronx. Methods: We conducted a retrospective review of a prospectively collected pediatric database for January-June 2019 in an inner-city teaching hospital. Information on gender, demographics, term/preterm, and birth weight was collected, in addition to follow-up weights at 2-, 4-, 6-, and 12-month visits. Growth of subjects was studied to evaluate weight-gain between visits; baseline weight was the birth weight used to compare the consecutive patterns and subgroup analysis was performed. Results: Charts of 98 infants were reviewed. The mean birth weight was 3.2±0.43 kg and 90% of the births were at term. Gender distribution was 54% male and 46% female. Overall demographics was distributed as follows: Hispanic were 48%, African American were 20% and 32% were other. Weight doubled in the group at 4 months in 57 patients (58%) and at 6 months-36 patients (37%), a 37% difference in doubling of weight at 4 months (p=0.0041). Differences in demographics for 4 months was AA-15 (27%) and HS-26 (46%), and at 6-months was AA-6 (17%) and HS-21 (58%), p= 0.2856. Subgroup analysis of infants that doubled their birth weight versus those that did not at 4 months, birth weight was not significant (3.24±0.36 vs. 3.42±0.48, p=0.068), at 2 months significance occurred (5.56±0.69 vs. 5.17±0.89, p=0.042) and significance continued at 4 months (7.27±0.78 vs. 6.38±0.75, p=0.0001), 6-months (8.25±0.92 vs. 7.3±0.86, p=0.0002) and 12-months (10.41±0.96 vs. 9.43±1.06, p=0.001), respectively. At 12 months, 70% of patients had tripled their weights. Conclusion: A 37% difference in doubling of weight at 4 months was noted in our pediatric population, possibly due to over feeding of infants. We suggest further study is needed to validate these results in other populations and determine the cause for our observation.