Abstract Introduction Exclusively breastfed (EBF) newborns wake more often at night than partially breastfed, or exclusively formula fed (EFF) newborns. Contextual factors during the first weeks of life related to these associations are understudied. We examined relationships among post-birth experiences, objectively-estimated sleep-wake patterns, and feeding practices through three weeks post-delivery. Methods English or Spanish speaking mothers (n=20) and their full-term (≥37wk), singleton infants were recruited from Phoenix, Arizona. Mothers were 32.7±5.1y, 30.0% identified as Hispanic, 20.0% with < high school degree, and 15.0% were enrolled in the federal Women, Infants, and Children program. Infants were born normal weight (2500-4000g) and without major complications. At three weeks post-delivery, infants wore a Micro Motionlogger (Ambulatory Monitoring Inc.) on their left ankle for five 24hr periods at three weeks of age. Mothers completed an accompanying sleep diary and an adapted Infant Feeding Practices Study-II questionnaire. Pearson correlations and t-tests examined relationships between nocturnal sleep-wake patterns and feeding practices at birth and 3-weeks post-delivery. Results At birth, all mothers attempted breastfeeding, 40.0% of infants received formula, and mean time for milk to come in was 2.7 days (range: 1-4). At three weeks, one mother was EFF, 55.5% (n=11) were EBF, and 40.0% (n=8) were mixed feeding. Infant sleep-wake patterns included midpoint of 2:40±1:01, long wake episode (≥5min) frequency of 5.8±2.3, longest sleep bout duration of 127.2±34.9min, WASO of 124.1±54.3min, and TST of 434.7±79.7min. Breastmilk feeding frequency was positively related to long wake episode frequency (r=.49, p=0.03) and WASO (r=.47, p=0.04), and negatively related to longest sleep bout (r=-.59, p=0.006). Formula feeding frequency was positively related to longest sleep bout (r=.58, p=0.007). Greater time for milk to come in was positively related to long wake episode frequency (r=.53, p=0.02) and WASO (r=.56, p=0.01), and negatively related to longest sleep bout (r=-.47, p=0.04). Receiving formula in the hospital was associated with later sleep midpoint (t[18]=3.2, p=0.005), regardless of current formula feeding. Conclusion Feeding experiences and ability to breastfeed during the first few days of life may play a role in the quality and patterning of actigraphy-estimated sleep among newborns. Future research should investigate whether these associations persist into later infancy. Support (If Any) National Institutes of Health / National Heart, Lung, and Blood Institute R01 HL147931