Four RCTs (n=1,886), 20 cohort studies and five cross-sectional studies were included. The size of treatment groups in RCTs ranged from 140 to 354.
The RCTs scored 5 to 8 out of 9 for validity; details of criteria not met by individual studies were reported. RCTs evaluated different types of pacifier use: use during tube feeding or for soothing versus no pacifier; use during the neonatal period versus use after four weeks postpartum; an education programme that emphasised avoidance of pacifier use versus use of pacifiers; and a baby-friendly hospital environment in which pacifiers were avoided versus unrestricted pacifier use. Three studies were in infants born at 36 weeks or later; one study was in preterm infants (23 to 33 weeks).
None of the RCTs reported a statistically significant difference in breastfeeding outcomes associated with pacifier interventions.
Seventeen of the 25 observational studies reported shortened duration or exclusivity of breastfeeding associated with pacifier use for all outcomes examined; eight studies reported no significant association for either all or some breastfeeding outcomes. Most studies controlled for multiple variables.