16.1% of U.S. Level III/IV NICU admissions were for very low birth weight (VLBW) newborns (Figure 2.1). Just five years later (2012), this percentage had fallen to 13.8%, while the proportion admitted that were normal birth weight newborns (2,500-3,999 grams) rose from 42.2% to 46.6%. This trend has continued. By 2017, the percentage of NICU admissions that were for VLBW newborns had further decreased to 12.7%, and the percentage for normal birthweight had increased to 48.0%. The expansion of neonatal intensive care—and the resulting hospital competition for newborns— seems to have led to the loss of regionalized systems of perinatal care, and is not only associated with increasing use of NICUs for larger newborns, but may also be linked to more VLBW newborns (all of whom should be cared for in a Level III/IV NICU) receiving care in lower level units.3 Figure 2.1. Trends in the Composition of Level III and IV NICU Admissions by Birth Weight (2007 to 2012) Year Admissions (%) A REPORT OF THE DARTMOUTH ATLAS PROJECT 17 0% 20% 40% 60% 80% 100% 500- 999 1000- 1499 1500- 1999 2000- 2499 2500- 2999 3000- 3499 3500- 3999 4000- 4499 4500- 4999 ≥ 5000 Cumulative Percent of Total NICU Admissions Admission Rate Very low birth weight Low birth weight Normal birth weight High birth weight Figure 2.2 shows the distribution of NICU-admitted newborns by birth weight. The blue line is the percent of newborns admitted to Level III/IV units. The chance of a NICU admission is highest for newborns 1,000-1,499 grams—85.6%—and then falls steeply to 3.4% for newborns 3,500-3,999 grams. The chance of a NICU admission is also higher for very large newborns. The green line is the cumulative percentage: the product of the risk of admission and the number of newborns. Small newborns have a very high risk of admission, but they are far fewer in number than larger newborns. This means that larger newborns dominate NICU admissions because of their high numbers, even though the admission risk for each newborn is low. Figure 2.2. Level III and IV NICU Admissions by Birth Weight (2012) This shift in the composition of NICU admissions to a greater proportion of higher weight and gestational age newborns has outpaced our knowledge about the effectiveness and value of the care they receive. Relatively little is known about care processes and outcomes for newborns greater than 1,500 grams, including whether the newborns being admitted are best cared for in a NICU environment— or whether there are newborns being cared for in Level II units who would do better if admitted to Level III/IV NICUs. At the same time, approximately 15% of newborns less than 1,500 grams are not admitted to a Level III/IV NICU despite evidence showing improved outcomes and reduced mortality when they are cared for in higher level units.4-6 Birth Weight (grams) Admissions (%) A Report of the Dartmouth Atlas Project 18 DARTMOUTH ATLAS OF NEONATAL INTENSIVE CARE Map 2.1. Admission Rates to Level III/IV NICUs among All Newborns by NICR (2013) Regional Variation in Level III/IV NICU Admission Rates7 For all newborns, the admission rate to NICUs varies markedly (Map 2.1). (Note that data are missing for the few states that had not yet adopted the revised CDC birth certificate that includes a field for NICU admission.) Admission rates are depicted as the ratio of the region’s rate to the overall rate for all reporting regions. Some variation is expected and warranted, given that perinatal risk factors, such as birth weight and socioeconomic status, also vary by states and regions. The data shown in Maps 2.2-2.4 partially control for regional differences in the health status of newborns by restricting to three birth weight categories: very low birth weight (VLBW) (500-1,499 grams), moderately low birth weight (1,500-2,499 grams), and normal birth weight (≥ 2,500 grams). A quick glance shows relatively little variation in NICU admissions for the sickest newborns (i.e., VLBW); almost all of them were admitted to NICUs regardless of the region (Map 2.2). The coefficient of variation was 10. For moderately low birth weight newborns (1,500-2,499 grams), high variation in NICU admissions was observed. Regions with low admission rates included Laredo, Texas (15.4%), Lansing, Michigan (16.4%), Richmond, Virginia (19.4%), Corpus Christi, Texas (20.7%), and Valdosta, Georgia (20.9%). Admission rates were more than three times higher than the lowest regions in Lincoln, Nebraska (60.9%), Stony Brook, New York (56.9%), Boise, Idaho (55.5%), Minneapolis, Minnesota (55.3%), and Rapid City, South Dakota (55.3%) (Map 2.3). The coefficient of variation was 20. The highest variation in regional NICU admission rates was seen in the normal birth weight (≥ 2,500 grams) newborns. Regions with low admission rates included Richmond, Virginia (1.6%), Laredo, Texas (1.7%), Valdosta, Georgia (1.7%), Roanoke, Virginia (1.8%), and Corpus Christi, Texas (1.8%). In the regions with the highest rates, including Newark, Delaware (9.2%), Alexandria, Louisiana (9.0%), El Paso, Texas (8.9%), Stony Brook, New York (8.3%), and Staten Island, New York (8.1%), admissions to NICUs were more than five times higher. The coefficient of variation was 34. Neonatal Intensive Care Regions Throughout the Atlas, analyses of newborn care are