Key messages
• Exposure to the smell and taste of milk with tube feeds may have little to no effect on the time it takes preterm infants to reach full sucking feeds.
• We found no evidence of any unwanted effects of exposure to the smell and taste of milk with tube feeds in newborn infants.
What is tube feeding?
Infants born preterm (before 37 weeks of pregnancy) often need to be fed via a thin tube inserted through the mouth (orogastric tube) or nose (nasogastric tube) into the stomach until they are able to suck all of their feeds.
Why is the smell and taste of milk important for tube-fed babies?
Initially, only small volumes of milk are given, and this is gradually increased depending on how well the babies tolerate the milk. Smell and taste have a significant role in helping with digestion and absorption of food, and since infants being fed by a tube may not experience the smell or taste of milk, they might be taking longer to tolerate larger volumes of milk.
What did we want to find out?
We wanted to find out if exposing infants to the smell and taste of milk before or while they were being fed through a tube could help them tolerate greater volumes of milk more quickly and improve their overall growth and development. We also wanted to know if this method had any unwanted effects.
What did we do?
We searched for studies that investigated exposing preterm infants to the smell or taste (or both) of milk with tube feeds, compared to no such exposure. We compared and summarised the results of the studies and rated the certainty of the evidence, based on factors such as study methods and number of infants included.
What did we find?
We identified eight completed studies involving 1277 preterm infants admitted to a neonatal intensive care unit.
Exposure to the smell and taste of milk with tube feeds may have little to no effect on the time to reach full sucking feeds, but the results are very uncertain. Two studies reported that no infants had any unwanted effects related to exposure to the smell and taste of milk with tube feeds. Exposure to the smell and taste of milk may have little to no effect on duration of intravenous nutrition (feeding through a vein), time to reach full enteral feeds (feeds though a tube into the stomach), or on the risk of necrotising enterocolitis (a serious intestinal disease), although the results for time to full enteral feeds are very uncertain. Exposure to the smell and taste of milk probably has little or no effect on the risk of developing an infection more than two days after birth.
What are the limitations of the evidence?
We have little confidence in the evidence because:
• we identified few studies;
• most studies were small and provided different types of exposure to smell and taste;
• in many studies, clinicians and parents were aware of which treatment the infant was receiving; and
• the studies did not investigate all the outcomes we were interested in.
How up-to-date is this evidence?
This review is current to April 2023.
The results of our meta-analyses suggest that exposure to the smell and taste of milk with tube feeds may have little to no effect on time to reach full sucking feeds and time to reach full enteral feeds. We found no clear difference between exposure and no exposure to the smell or taste of milk on safety outcomes (adverse effects, necrotising enterocolitis, and late infection).
Results from one ongoing study and two studies awaiting classification may alter the conclusions of this review. Future research should examine the effect of exposing preterm infants to the smell and taste of milk with tube feeds on health outcomes during hospitalisation, such as attainment of feeding skills, safety, feed tolerance, infection, and growth. Future studies should be powered to detect the effect of the intervention in infants of different gestational ages and on each sex separately. It is also important to determine the optimal method, frequency, and duration of exposure.
Preterm infants (born before 37 weeks' gestation) are often unable to co-ordinate sucking, swallowing, and breathing for oral feeding because of their immaturity. In such cases, initial nutrition is provided by orogastric or nasogastric tube feeding. Feeding intolerance is common and can delay attainment of full enteral and sucking feeds, prolonging the need for nutritional support and the hospital stay. Smell and taste play an important role in the activation of physiological pre-absorptive processes that contribute to food digestion and absorption. However, during tube feeding, milk bypasses the nasal and oral cavities, limiting exposure to the smell and taste of milk. Provision of the smell and taste of milk with tube feeds offers a non-invasive and low-cost intervention that, if effective in accelerating the transition to enteral feeds and subsequently to sucking feeds, would bring considerable advantages to infants, their families, and healthcare systems.
To assess whether exposure to the smell or taste (or both) of breastmilk or formula administered with tube feeds can accelerate the transition to full sucking feeds without adverse effects in preterm infants.
We conducted searches in CENTRAL, MEDLINE, Embase, CINAHL, and Epistemonikos to 26 April 2023. We also searched clinical trial databases and conference proceedings.
We included randomised and quasi-randomised studies that evaluated exposure versus no exposure to the smell or taste of milk (or both) immediately before or at the time of tube feeds.
Two review authors independently selected studies, assessed risk of bias, and extracted data according to Cochrane Neonatal methodology. We performed meta-analyses using risk ratios (RRs) for dichotomous data and mean differences (MDs) for continuous data, with their respective 95% confidence intervals (CIs). We used GRADE to assess the certainty of evidence.
We included eight studies (1277 preterm infants). Seven studies (1244 infants) contributed data for meta-analysis.
The evidence suggests that exposure to the smell and taste of milk with tube feeds has little to no effect on time taken to reach full sucking feeds (MD −1.07 days, 95% CI −2.63 to 0.50; 3 studies, 662 infants; very low-certainty evidence). Two studies reported no adverse effects related to the intervention. The intervention may have little to no effect on duration of parenteral nutrition (MD 0.23 days, 95% CI −0.24 to 0.71; 3 studies, 977 infants; low-certainty evidence), time to reach full enteral feeds (MD −0.16 days, 95% CI −0.45 to 0.12; 1 study, 736 infants; very low-certainty evidence) or risk of necrotising enterocolitis (RR 0.93, 95% CI 0.47 to 1.84; 2 studies, 435 infants; low-certainty evidence), although the evidence for time to reach full enteral feeds is very uncertain. Exposure to the smell and taste of milk with tube feeds probably has little to no effect on risk of late infection (RR 1.14, 95% CI 0.74 to 1.75; 2 studies, 436 infants; moderate-certainty evidence). There were no data available to assess feeding intolerance.
The included studies had small sample sizes and methodological limitations, including unclear or lack of randomisation (four studies), lack of blinding of participants and personnel (five studies), unclear or lack of blinding of the outcome assessor (all eight studies), and different inclusion criteria and methods of administering the interventions.