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In the United States, breastfeeding initiation rates have risen to 80%.1 We report secular trends of breastfeeding initiation and duration by birth weight using nationally representative data from the National Health and Nutrition Examination Survey (NHANES).
The NHANES is a complex, stratified, multistage probability sample of the US civilian noninstitutionalized population, conducted by the National Center for Health Statistics, Centers for Disease Control and Prevention. The NHANES was approved by the National Center for Health Statistics Research Ethics Review Board.
Using data from 13 859 children ages 0 to 6 years who participated in the NHANES from 1999 to 2014, we constructed birth year cohorts (1997-2000, 2001-2004, 2005-2008, and 2009-2012) and birth weight categories (<2500 g [low birth weight (LBW)], ≥2500 g). Birth weight and breastfeeding history (ever breastfed or received breast milk) were obtained by proxy interview, most commonly by a parent.2 The unweighted response rate ranged from 77% to 93%.3 Written parental consent was obtained for those younger than 18 years.
We estimated the proportion of infants ever breastfed (initiated) and those reporting any breastfeeding at 1 month, 4 months, and 6 months by birth weight categories and birth year cohorts. Infants were excluded if they had not attained the age at which breastfeeding was being estimated. Significance was set at α < .05 for adjusted Wald method and orthogonal contrast matrices for linear tests of trends over time. Taylor series linearization was used for variance estimation and 95% CIs were computed by the Wald method. Kaplan-Meier curves and log-rank tests assessed differences in the duration of breastfeeding by birth weight cohort from 2009 to 2012. LOESS smoothed curves and 95% CIs from Kaplan-Meier curves are presented. Infants were censored at the time of interview if they were currently receiving breast milk (12% of respondents, unweighted n = 324). Overall, 8% of infants were LBW (unweighted n = 1279).
SAS version 9.3 (SAS Institute) and SUDAAN version 11.0 (RTI International) were used. Survey design variables and interview sample weights, which account for differential probabilities of selection, nonresponse, noncoverage, and sample design, were used to obtain estimates representative of the civilian noninstitutionalized US population.
Among all infants, breastfeeding initiation rates increased from 65.7% (95% CI, 62.4%-69.1%) in 1997-2000 to 76.7% (95% CI, 73.5%-79.8%) (P < .001) in 2009-2012. Over the same period, breastfeeding initiation rates increased from 48.8% (95% CI, 39.6%-57.9%) to 65.4% (95% CI, 55.4%-75.3%) (P = .01) for LBW infants and from 67.4% (95% CI, 64.0%-70.8%) to 77.5% (95% CI, 74.3%-80.8%) (P < .001) for infants weighing 2500 g or more at birth (Table). An increasing secular trend in the percentage of infants still breastfeeding at 1 month (59.7% [95% CI, 56.2%-63.2%] to 68.7% [95% CI, 65.0-72.4%]; P < .001), 4 months (42.6% [95% CI, 39.3%-46.0%] to 49.6% [95% CI, 45.6%-53.7%]; P = .005), and 6 months (36.2% [95% CI, 33.0%-39.5%] to 43.1% [95% CI, 39.3%-47.0%]; P = .002) was observed for infants weighing 2500 g or more. For LBW infants, the increase in the percentage still breastfeeding over time was not significant at any time after birth. This is likely owing to insufficient power arising from the small sample of LBW infants.
Within each birth cohort, the percentage of infants initiating breastfeeding and breastfeeding at 1, 4, and 6 months was significantly smaller for LBW infants compared with their heavier counterparts. For example, in 2009-2012, 43.1% of infants (95% CI, 39.3%-47.0%) weighing 2500 g or more were breastfeeding at 6 months compared with 27.7% of LBW infants (95% CI, 18.2%-37.2%) (P < .001). The only exception was among those still breastfeeding at 1 month in 2001-2004; this difference was not statistically significant.
The Figure presents the smoothed Kaplan-Meier curves for the overall duration of breastfeeding in the first year of life by birth weight categories. Infants who never breastfed were censored at time zero. Among infants born in 2009-2012, LBW infants had a 38% (95% CI, 1.17-1.63) increased hazard of discontinuing breastfeeding compared with infants weighing 2500 g or more (P < .001).
Data derived from National Health and Nutrition Examination Survey,2 birth cohort 2009-2012. Estimates derived from PROC KAPLANMEIER and plotted using LOESS. The number at risk is calculated from unweighted data and is therefore not directly comparable with the smoothed LOESS values in the plot.
Although breastfeeding rates have increased over the past 2 decades, the percentage of LBW infants ever breastfed and continuing to breastfeed was lower than infants weighing 2500 g or more. These baseline estimates may be used to track current and future public health efforts.
Corresponding Author: Kirsten A. Herrick, PhD, MSc, Division of Health and Nutrition Examination Surveys, National Center for Health Statistics, Centers for Disease Control and Prevention, 3311 Toledo Rd, Hyattsville, MD 20782 (firstname.lastname@example.org).
Published Online: June 27, 2016. doi:10.1001/jamapediatrics.2016.0820.
Author Contributions: Dr Herrick had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: All authors.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: Herrick, Rossen.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: All authors.
Administrative, technical, or material support: Rossen, Kit, Wang.
Study supervision: Ogden.
Conflict of Interest Disclosures: None reported.
Disclaimer: This work was performed under employment of the US federal government and the authors did not receive any outside funding. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the National Center for Health Statistics, Centers for Disease Control and Prevention.
Herrick KA, Rossen LM, Kit BK, Wang C, Ogden CL. Trends in Breastfeeding Initiation and Duration by Birth Weight Among US Children, 1999-2012. JAMA Pediatr. 2016;170(8):805–807. doi:10.1001/jamapediatrics.2016.0820
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