Growth charts! They are a huge topic, partly because of many opinions on them. There are good reasons why there are so many opinions on them. One thing to keep in mind, believe it or not, is that they are not all the same. The growth chart I use vs the one some doctors use vs public health vs all the apps is that some use older versions that were made and provided by formula companies, some use the CDC, some use the WHO, and some maybe even have their own.
Once upon a time, I was trained to not really consider what growth charts said because the ones we had were made in the 1970s/1980s with a group of all American Caucasian formula fed babies and they were distributed to health care providers by formula companies. Because of this, it was believed they had no relevance to breastfed babies. This isn't entirely wrong, but this is also no longer the case.
The growth charts available today have since been redesigned. The WHO one is now based on breastfed, world wide babies with much more detailed analysis. I will point out there are many growth chart versions available - so please look to see what is being referenced. With proper understanding they can be a very useful tool and tell *part* of the story of growth. The WHO developed standards of growth of the breastfed infant as the norm for growth. The WHO charts reflect growth patterns among children who were predominantly breastfed for at least 4 months and still breastfeeding at 12 months. In contrast, the CDC growth charts are references. They identified how typical children in the US DID grow during a specific time period. Typical growth patterns may not be ideal growth patterns. I often say "just because something is common, does not mean it is normal." The WHO growth charts are standards; they identify how children should grow when provided optimal conditions. The WHO standards are based on a high-quality study designed specifically for creating these growth charts. For the CDC growth charts, weight data were not available between birth and 3 months of age and the sample sizes were small for sex and age groups during the first 6 months of age. There are lots of gaps in these charts! Some infant apps actually use their own version!
It is still common to hear statements like “don’t worry about it” but sometimes this is secret code for “I don’t know how to help you” or “I don’t know how to read the data” or “I don’t understand what the chart is telling me”.