Facial Expressions in Small for Gestational Age Newborns

In a recent article published in the Journal of Child Neurology, Rotstein et al suggest that there is no difference in the facial recognition patterns for taste between small for gestational age and control newborns, except for the perception of distilled water. Nonetheless, when analyzing their Figure 1A, it seems to us that this result regarding water versus sucrose facial expressions resembles very much the one we described previously. We evaluated 1-day-old preterm infants that received 24% sucrose solution or water on the taste reactivity test, and we found a highly positive correlation between fetal growth and the hedonic response in the group exposed to the sweet solution but not in the group exposed to water. In other words, the more intense the intrauterine growth restriction, the lower the frequency of the hedonic response observed, suggesting that intrauterine growth restriction is linked to a decreased sensitivity to the enjoyment elicited by the sweet taste. However, because our results derived from a clinical trial, we were not able to compare the same child’s response across different trials, as Rotstein et al could. Water is tasteless and odorless and therefore to us the pattern of response to water should be considered as a baseline or simple motor response. If Rotstein et al had studied the response using a sucrose to water ratio in each group, the expected pattern of reactivity in control children becomes clear, which almost double the hedonic response when tasting the sucrose solution in relation to water. On the other hand, the same ratio in small for gestational age children would be near to one, suggesting that they were unable to recognize the pleasurable sensation associated with sugar. The authors interpreted the finding as if the control group had a decreased perception for water and attributed this odd finding to ‘‘an artifact due to multiple comparisons. ’’ To us, this is a simple misinterpretation of the data. The main question then becomes why is there such a discrete response to the other solutions tested (quinine, citrate). A possible explanation is that the ‘‘dislike’’ side of the scale has a worse discerning ability. Another question is why small for gestational age children have an increased baseline response to water when compared to controls; however, this is easily explained by a peculiar motor development in small for gestational age infants, which has been extensively described, and likely to be present already at birth. Besides using the response to distilled water as a baseline in the Rotstein et al study, it would have been interesting to see if there is a continuous correlation between birth weight and the response scale values; for that, they could have used the birth weight ratio (observed birth weight divided by the mean population birth weight specific for sex and gestational age) as we did in our study. Rotstein and colleagues’ findings reassure us about the idea that small for gestational age infants have indeed a difficulty in discriminating plain water from the sucrose flavor, as seen in our study. We propose that this inability to detect the pleasurable sensation associated with sugar predisposes them to develop an increased consumption of palatable foods later in life, as we and others have described. The increased preference for palatable foods could be an important factor contributing to the development of obesity and its metabolic consequences in the small for gestational age population. As intrauterine growth restriction is often seen in a context of social vulnerability and poor food security, the fetal programming of food preferences is an essential topic in preventive research.