by Anne Eglash MD, IBCLC, FABM
Does the smell of mother’s milk help reduce procedural pain in newborns? Studies show that infants by the age of 28 weeks gestation have a sufficient sense of smell that they are able to distinguish an odor of amniotic fluid. Further, amniotic fluid and human milk have several fatty acids in common that create a similar odor between the two. Various studies have shown that the odor of maternal milk may help to alleviate an infant’s pain during blood drawing.
Authors of a recent meta-analysis sought to evaluate the strength of this evidence. They selected 8 randomized controlled trials involving 453 newborns, including 303 premature infants and 150 term infants. All studies involved blood sampling, either heel sticks or venipuncture, on the infants.
The infants were exposed to 1ml-10ml of human milk to smell during the procedure. The studies compared the infant’s pain response to either the scent of vanilla, the scent of amniotic fluid, the scent of formula, or no scent.
The pain response was measured differently in the 8 studies. Measurements included either the duration of crying, mean oxygen saturation after the procedure, level of salivary cortisol after the blood draw, heart rate, pain scores, or heart rate variability.
What do you think the authors found regarding the ability for mother’s milk odor to reduce pain in infants undergoing a blood draw? Choose 1 or more:
- Infant pain scores were significantly lower in the maternal milk odor group than the scentless group.
- There was no significant difference in the duration of crying among newborns during a blood draw when exposed to human milk odor vs either vanilla, amniotic fluid, or no scent.
- Infant pain scores were significantly lower in the maternal milk odor group compared to the amniotic fluid group.
- The infants exposed to human milk odor had significantly lower salivary cortisol levels post blood draw compared to those exposed to formula odor.
See the Answer
The answers are A, B, D (not C)
The Analgesic Effects of Maternal Milk Odor on Newborns: A Meta-Analysis
Shiyi Zhang, fang Su, Jing Li, Weiju Chen
The objective of this study was to evaluate the analgesic effects of maternal milk odor on newborns.
Materials and Methods:
We searched the literature in PubMed, MEDLINE, CINAHL, EMBASE, Web of Science, and the Cochrane Central Register of Controlled Trials (CENTRAL) and collected all the randomized controlled trials (RCTs) investigating the effects of maternal milk odor versus scentless or other odors on procedural pain in newborns. The quality of included studies was assessed by the Cochrane Collaboration Risk of Bias tool. A meta-analysis was undertaken with the Review Manager 5.3 software and Stata version 11.0. Subgroup comparisons were prespecified according to the types of control groups.
Eight RCTs included a total of 453 participants. The results of meta-analysis showed that compared with the scentless group, the maternal milk odor group had lower pain scores during blood sampling (standardized mean difference, −0.81; 95% confidence interval [95% CI], −1.18 to −0.44; p < 0.001) and shorter crying time afterward (mean difference, −8.10; 95% CI, −15.46 to 0.73; p = 0.03). The maternal milk odor group had lower heart rate variability and oxygen saturation variability during and after a procedure, compared with both the scentless group and the vanilla group. However, no significant difference was identified in the mean heart rate and mean oxygen saturation in terms of the maternal milk odor group compared with amniotic fluid odor or mother's scent. The maternal milk odor group versus the formula milk odor group had shorter crying duration and lower levels of salivary cortisol after sampling.
Maternal milk odor appears to play an analgesic role in newborns. However, more high-quality studies are needed to confirm and quantitate the effect.
Milk Mob Comment by Anne Eglash MD, IBCLC, FABM
It appears convincing that the odor of mother’s milk can have an analgesic quality on infants during a heel stick or a venous blood draw. However, the studies had several different ways of measuring ‘analgesia’, so it was hard to compare the studies to each other, and not all measurements of analgesia showed an effect.
For practical purposes, the methods of presenting the human milk odor were by using an odor diffuser, or by placing drops of milk on either a sterile sponge, filter paper, cotton pad or an Ookie doll.
We reviewed best strategies to control pain for a breastfeeding infant in Clinical Question #18 (link to https://lacted.org)
The good news is that using the odor of mother’s milk can be added to other proven strategies to decrease an infant’s procedural pain, including sensorial stimulation, skin-to-skin, direct breastfeeding, administration of breastmilk, and oral sucrose solution.