Key messages
-
Introducing preterm infants to the smell of maternal breast milk may slightly reduce the time it takes for them to feed fully by mouth. Introducing them to food smells such as vanilla and cinnamon may slightly reduce how often they stop breathing. Finally, introducing preterm babies to the smell of rose or a parent's scent may reduce slightly the time they have to stay in hospital. All other results are very uncertain.
-
Future studies should include more infants, use more rigorous designs, and measure outcomes such as breathing problems, low blood oxygen levels, exclusive breastfeeding, and long-term neurodevelopmental outcomes.
What is preterm birth?
A normal pregnancy usually lasts from 37 weeks to 42 weeks. Preterm birth is when a baby is born before 37 weeks of pregnancy. Babies born preterm have not had enough time to fully develop before birth. Their organs may not yet be ready to work on their own, which means they often need intensive medical care and are at greater risk of breathing and feeding difficulties, infection, and problems that can affect their long-term development.
What is olfactory stimulation, and how does it work?
Preterm infants often take time to build up the skills or physical capacity to feed by mouth, and in the meantime are fed through a tube passed into the stomach. Olfactory stimulation involves introducing smells to preterm infants while they are in hospital to see if it helps them start breastfeeding more quickly. These smells include breast milk, food smells such as vanilla or cinnamon, and other smells such as a floral scent or a parent's scent.
What did we want to find out?
We wanted to find out whether introducing a smell to preterm infants in hospital could be helpful and safe for their short-term and long-term well-being. More specifically, we wanted to find out whether introducing a smell to preterm infants is better than placebo (dummy treatment), no treatment, or usual care for:
-
reducing the number of infants who have apnea (brief pauses in breathing);
-
reducing the number of infants with low oxygen levels in the blood;
-
reducing the time spent in hospital;
-
reducing the time needed for the infants to learn to feed fully by mouth;
-
increasing the number of infants that are fed only with breast milk;
-
reducing the number of infants with blindness or deafness between 18 and 24 months of age.
What did we do?
We searched for studies that compared olfactory stimulation with placebo, no treatment, or usual care in preterm infants.
We summarized the results of the studies and rated our confidence in the evidence based on factors such as study size (number of infants) and methods.
What did we find?
We included 14 studies with 1087 infants. Nine studies used the smell of maternal breast milk, five used food-associated smells (vanilla, cinnamon, or anise), and three studies used other smells (rose or parents' scent). All studies compared these smells with no treatment, placebo, or usual care.
Main results
Introducing the smell of maternal breast milk may reduce slightly the time it takes infants to feed fully by mouth. It is unclear whether stimulation with this smell has any effect on how often infants have apnea episodes and how long they stay in hospital.
Introducing the smell of cinnamon, vanilla, or anise may slightly reduce how often infants have apnea episodes. It is unclear whether stimulation with these smells has any effect on how long infants stay in hospital or how long it takes them to feed fully by mouth.
Introducing the scent of rose or a parent's scent may slightly reduce how long infants spend in hospital. It is unclear whether stimulation with these smells has any effect on how often infants have apnea episodes or how long it takes them to feed fully by mouth.
What are the limitations of the evidence?
We have little confidence in these results, as the studies included could have been better designed and included more babies. Several studies did not report outcomes we were interested in.
How up to date is this evidence?
The evidence is current to 2 April 2025.
Baca abstrak penuh
Matlamat
To evaluate the benefits and harms of olfactory stimulation for reducing morbidity and promoting development in hospitalized preterm infants.
Kaedah Pencarian
We searched MEDLINE, Embase, CENTRAL, CINAHL, Epistemonikos, two trial registries, and conference abstracts up to 2 April 2025. We checked the reference lists of included studies and systematic reviews on olfactory or sensory stimulation.
Kesimpulan Pengarang
Olfactory stimulation with maternal breast milk compared to no intervention, placebo, or standard care may result in a slight reduction in time to full oral feeding, but the evidence is very uncertain about its effect on frequency of apnea episodes and duration of hospital stay. Olfactory stimulation with food-associated odors compared to no intervention, placebo, or standard care may result in a slight reduction in frequency of apnea episodes, but the evidence is very uncertain about its effect on duration of hospital stay and time to full oral feeding. Olfactory stimulation with non-food-associated odors compared to no intervention, placebo, or standard care may result in a slight reduction in duration of hospital stay, but the evidence is very uncertain about its effect on frequency of apnea episodes and time to full oral feeding.
Future studies should be more rigorous in their design, report using TIDieR (Template for Intervention Description and Replication) checklists, have larger sample sizes, and measure outcomes such as apnea (number of infants with ≥ 1 episode), intermittent hypoxemia (number of infants with ≥ 1 episode), exclusive breastfeeding, and major neurodevelopmental disabilities.
Pembiayaan
Dedicated funding for this review can be found in the 'Sources of support' section.
Pendaftaran
Protocol: https://doi.org/10.1002/14651858.CD016074.
