Abstract: Three trials involving a total of 161 preterm infants were included in this review, but only two trials (131 infants) contributed data for meta-analysis. There was no evidence of a clear effect of exposure to the smell and taste of milk with tube feedings on time taken to reach full sucking feeds (MD -2.57 days, 95% CI -5.15 to 0.02; I2 = 17%; 2 trials, 131 infants; very low-quality evidence). One trial reported no adverse effects. There was no evidence of a clear effect of exposure to the smell and taste of milk on the following outcomes: time taken to reach full enteral feeds (MD -1.57 days, 95% CI -6.25 to 3.11; 1 trial, 51 infants; very low-quality evidence), duration of parenteral nutrition (MD -2.20 days, 95% CI -9.49 to 5.09; 1 trial, 51 infants; very low-quality evidence), incidence of necrotising enterocolitis (RR 0.62, 95% CI 0.15 to 2.48; 1 trial, 51 infants; low-quality evidence), and late infection (RR 2.46, 95% CI 0.27 to 22.13; 1 trial, 51 infants; low-quality evidence). There was very low-quality evidence demonstrating that exposure to the smell and taste of milk decreased duration of hospitalisation by almost four days (MD -3.89 days, 95% CI -7.03 to -0.75; I2 = 51%; 2 trials, 131 infants). In two trials, an increased growth velocity was noted in infants exposed to the intervention, but we were unable to combine data to perform meta-analysis. No data were available to assess feed intolerance and rates of exclusive breastfeeding at discharge. Included trials were small and had methodological limitations including lack of randomisation (one trial), lack of blinding, and different inclusion criteria and administration of the interventions. Evidence from two trials suggests that exposure to the smell and taste of milk with tube feedings has no clear effect on time taken to reach full sucking feeds, but it may decrease length of hospitalisation. However, these results are uncertain due to the very low quality of the evidence. There is also limited evidence about the impact on other important clinical outcomes and on safety. Future research should examine the effect of exposure to the smell and taste of milk with tube feedings on clinical outcomes during hospitalisation, such as attainment of full enteral and sucking feeds, safety, feed tolerance, incidence of infection, and infant growth. Additionally, future research should be sufficiently powered to evaluate the effect of the intervention in infants of different gestational ages, on each sex separately, and on the optimal frequency and duration of exposure.

Plain-language summary: In a search up to 1 June 2018, we identified three completed studies involving 161 preterm infants admitted to a neonatal intensive care unit (NICU) at a tertiary hospital. One study involved 51 preterm infants, and each infant had an equal chance of being chosen to receive either treatment (a randomised controlled trial). One study involved 80 preterm infants who were sequentially assigned to control and treatment groups (a quasi-randomised trial). One study was a prospective randomised trial involving 30 infants, but the way it was reported meant there was not enough information for us to include in our analyses. We found that exposure to the smell and taste of milk with orogastric or nasogastric tube feedings had no clear effect on the time to reach full sucking feeds. One study reported no adverse effects. Exposure to the smell and taste of milk also had no clear effect on time to reach full tube feeding, feed tolerance, incidence of late infection and severe intestinal infection, duration of intravenous nutrition, and growth. Very low-quality evidence from two studies suggested that exposure to the smell and taste of milk decreased the length of hospital stay by almost four days compared to no exposure to the smell and taste of milk. However, the included studies were small and had several limitations in terms of how they were done. Exposure to the smell and taste of milk with orogastric or nasogastric tube feedings may decrease length of hospitalisation for preterm infants. However, the effect of this treatment to accelerate feeding in preterm infants is uncertain due to limited and very low-quality evidence. Future research needs to explore the effect of exposure to the smell and taste of milk with tube feedings on important clinical outcomes, such as time to full sucking feeds, adverse effects, time to reach full tube feedings, feed tolerance, incidence of infection, and growth.