Repeated and untreated pain can lead to long-term consequences in preterm infants, such as pain hypersensitivity and impaired motor and intellectual development. Studies on the pharmacological and non-pharmacological interventions for pain management in preterm infants are limited. Thus, we investigated an intervention based on olfactive stimulation with mothers' milk. The aims of this study are: a) Evaluate the effectiveness of an olfactive stimulation intervention with mothers' milk odor on preterm procedural pain; b) Evaluate the effectiveness of adding a period of familiarization previous to the olfactive stimulation intervention with mothers' milk odor on preterm procedural pain. Preterm infants will be recruited and randomly assigned to three groups 1) mothers' milk odor during the nine hours before and during heel-prick, 2) mothers' milk odor during heel-prick, 3) standard care. Pain will be measured using a scale of pain adapted for preterm infants. This procedure with mothers'milk odor is inexpensive and easily performed.This study will significantly contribute to the advancement of knowledge on preterm infants pain management.

Inclusion Criteria for mothers

• 18 years or older,
• speak, understand and write French or English
• express their milk

Exclusion Criteria for mothers

- pathology or condition that contraindicates the use of their breast milk (HIV, drugs...)

Inclusion Criteria for preterm

• 29 to 36 weeks of gestation
• APGAR > 6 at 5 minutes
• less than 21 days

Exclusion Criteria for preterm

• intubated, under Continuous Positive Airway Pressure or nasal oxygen,
• surgery in the first day of life
• congenital disease
• intraventricular hemorrhage > grade II
• leukomalacia
• sedation within 48 hours prior to heel prick
• pharmacologic treatment for pain within 12 hours prior to heel prick
• being under phototherapy treatment during the familiarization stage