The objective of this randomized, single-blind clinical trial is to compare the efficacy of two treatments (Myofunctional Therapy and breastfeeding sessions) in infants who have difficulty breastfeeding during the first week of life.

The main questions to be answered are:

• Is breastfeeding improved with this type of intervention?
• What type of intervention is better?
• After carrying out these interventions, does the baby need to undergo surgery if it presents a sublingual frenulum? Participants must be infants who are one week old and who have been diagnosed with ankyloglossia through the Hazelbaker Scale. They will be randomly distributed into the two intervention groups and after one month of treatment, they will be assessed again using the same scale.

The researchers will compare the results between these two groups in order to verify the best intervention.

Infants who met the inclusion and exclusion criteria, respectively, were accepted to participate in the study. The randomization of the sample was performed by a statistician, who had no prior contact with either the infants or the parents. The online Randomizer (www.randomizer.org) program was used to randomly generate 200 sets of numbers, each containing two numbers ranging from 1 to 2 in random order. After signing the consent, a code was randomly chosen for each patient, thus ensuring that the 200 patients were equally distributed into two groups according to the group number of each code: group 1 (Myofunctional Therapy group) and group 2 (group sessions lactation).

Infants who met the inclusion criteria were referred to the rehabilitation and physiotherapy service. A physical therapist outside the study was in charge of evaluating the measurements of all infants during the first week of life through all the scales detailed below (pre-test). After randomly assigning the infants, another physiotherapist was responsible for applying the intervention once a week for 30 minutes for a period of 30 days. Once the intervention was finished, all the infants (both intervention groups) were reassessed by the physiotherapist outside the study using the same baseline scales (post-test).

Inclusion Criteria:

• Full-term infants exclusively breastfed
• Born both by normal delivery and by cesarean section
• Who presented difficulty in breastfeeding

Exclusion Criteria:

• Preterm newborns
• With low birth weight (less than 2,500 kg)
• Mothers with flat or inverted nipples
• Patients who did not wish and did not authorize to participate in the study.

A physiotherapist outside the study was in charge of carrying out the first evaluation in the first week of life of the infant. Another physiotherapist was in charge of applying the physiotherapy intervention. After completion of the intervention, all infants were reassessed by another physiotherapist outside the study.