Low birthweight causes many health challenges for newborns in the days and months after their birth and serves as a strong predictor for future health issues such as developmental problems, cardiovascular disease, and respiratory conditions. Low birth weight is also an indicator of the health of the mother during pregnancy and of the accessibility of maternal health resources. A child is categorized as having a low birth weight if the weight at birth is less than 2,500 grams.
Louisville currently ranks 8th among its peer cities on this metric, with 9.4% of infants being born at a low birthweight.
Louisville is in the middle tier of its peer group for low birth weight rates according to a natural breaks algorithm. Cities in green are those that outperform their peers, cities in yellow represent the middle cluster, and those in red are a group that lags behind its peers on this indicator.
The percent of babies born underweight has fluctuated between 9% and 10% over the past 15 years, and Louisville has been roughly close to the peer mean since 2008. While more years of data are needed to confirm a trend, the most recent year of data shows that Louisville might be improving compared to its peers and reducing the number of babies born with a low birthweight.
While underweight births in Louisville and the peer average have remained relatively constant, some cities have seen larger changes. Grand Rapids saw the largest increase in underweight births since the beginning of the data, and Knoxville saw the larges decrease in underweight births.
There is a very large disparity in the percent of babies born underweight to Black mothers and to white mothers. The percent of underweight births for Black mothers in Louisville is roughly double the rate for white mothers in Louisville. Since 2014, the rate of underweight births has increased for Black mothers, while the rate of underweight births has decreased for white mothers.
Female babies are about 25% more likely to be born underweight than male babies. The discrepancy in underweight births for male and female babies in Louisville largely follows the trends seen in peer cities.
For each indicator, Greater Louisville Project assigns cities into one of three groups (high-performing, middle-of-the-pack, and low-performing) based on how they compare to other cities. The assignment is based on how cities naturally cluster on that indicator. Sometimes, the differences between cities are very small, and the difference between a city ranked 5th and 6th could simply be a matter of the sampling error that arises from using survey data. Thus, rather than always make a division that declares the top 5 to be the top tier, we use a natural breaks algorithm to look for a cluster of cities that is outperforming the rest, a cluster that is about average, and a cluster that is lagging. This clustering gives us a better indication of where Louisville is thriving and where Louisville has room to learn from cities that are doing better.
Z-scores (or standardization) is a way to combine data with different units of measurement into a single index. The z-score is a measure of how far away a city (or census tract, etc.) is from the average city. In order to be comparable across different units of measurement, the z-score is the distance from the mean measured in standard deviations (e.g. if Louisville has a z-score of 1 it means Louisville is 1 standard deviation above the mean of its peer cities).
Data from the Robert Wood Johnson Foundation's County Health Rankings use z-scores and all z-scores are relative to the mean of Louisville's peer cities. (On the County Health Rankings site z-scores are relative to all the counties in each state - thus z-scores reported by GLP will be different, because we are using a different reference group). The Greater Louisville Project also uses z-scores in our multidimensional poverty index, which compares each census tract to the mean of all census tracts in Louisville.
