From a study by Butt ML, and Kisilevsky BS:
The physiological and behavioural effects of music during recovery from heel lance were examined in 14 preterm infants at 29 to 36 weeks post-conceptual age (PCA). Infants were tested on 2 occasions: during a music condition and during a no-music control condition. Each condition was videotaped during 3 periods: baseline, heel lance, and recovery. Infants were divided into 2 age groups for data analyses: less than and greater than 31 weeks PCA. Mixed model ANOVAs showed that heel lance elicited a stress response (i.e., increased heart rate, decreased oxygen saturation, increased state-of-arousal, and increased facial actions indicative of pain) in both age groups. The stress response was greater in the older group. During recovery, the older group had a more rapid return of heart rate, behavioural state, and facial expressions of pain to baseline levels in the presence of compared to the absence of music. It was concluded that music is an effective NICU intervention following a stress-provoking stimulus in infants older than 31 weeks PCA [emphasis added].
If you or someone you know has an infant in the NICU, you may want to try asking your doctor whether playing music to your infant might be a good idea. Based on previous research, the most effective music will be Mozart, preferably something with violins. Premature infants have it hard enough, and anything we can do to make their lives better will be worth it–and you can get classical music for free, if you look for it.