| | Study | Covariates |
| | Abad et al. [34] | N/A | | Altun-Köroğlu et al. [35] | N/A | | Bilgen et al. [36] | N/A | | Bucher et al. [37] | Sex, nurse, number of lances needed, baseline heart rate, and activity | | Campos [38] | The number of additional sticks required to obtain the blood sample, the duration of the heel stick, the frequency of crying, and the average HR | | Cong et al. [40] | N/A | | Cong et al. [39] | N/A | | Craig et al. [24] | N/A | | de Jesus et al. [41] | Gestational age, birth weight, sex, mode of delivery, diabetic mothers, breast-fed one hour before puncture, and received oral glucose | | de Oliveira et al. [42] | PIPP score in the period before the heel prick | |
Gormally et al. [43] | Preintervention baseline (percentage of time crying in the last two minutes before beginning the interventions) | | Goubet et al. [44] | N/A | | Gray et al. [45] | N/A | | Greenberg [46] | Age, weight, time since last feeding, heel stick and blood collection procedure length, and gestational age | | Grunau et al. [25] | Corrected chronological age | | Haouari et al. [47] | N/A | | Jatana et al. [48] | N/A | | Johnston et al. [49] | Apgar scores at 5 minutes, gestational age at birth, time since last painful procedure, number of painful procedures since admission, or received indomethacin in the past 12 hours | | Johnston et al. [50] | Frequency of invasive procedures, severity of illness, ventilation status, and sex | | Kostandy et al. [51] | N/A | | Leite et al. [52] | N/A | | Lindh et al. [55] | N/A | | Lindh et al. [54] | N/A | | Lindh et al. [53] | N/A | | Lucas-Thompson et al. [56] | Number of prior heel sticks, duration of blood draws, sex, and baseline heart rate | | Oberlander et al. [57] | Breast-fed, SSRI exposure, age at time of acute pain, maternal analgesia, dose of SSRI at delivery, and dose of clonazepam at time of delivery | | Oberlander et al. [58] | Breast-fed, SSRI exposure, age at time of acute pain, maternal analgesia, dose of SSRI at delivery, and dose of clonazepam at time of delivery | | Oberlander et al. [59] | N/A | | Ors et al. [60] | N/A | | Owens and Todt [61] | Sex | | Sajedi et al. [62] | Sex | | Shibata et al. [63] | N/A | | Singh et al. [27] | N/A | | Stevens et al. [65] | N/A | | Stevens and Johnston [64] | N/A | | Taksande et al. [66] | N/A | | Upadhyay et al. [67] | N/A | | Uyan et al. [68] | N/A | | Walden et al. [69] | N/A | | Weissman et al. [70] | N/A | | Weissman et al. [71] | N/A |
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