In the United States in 2015, of more than 4 million births, 6.9 percent weighed 4000 to 4499 g; 1 percent weighed 4500 to 4999 g; and 0.1 percent were born weighing 5000 g or more 4500-4649 3221 (Martin, 2017) . To be sure, the incidence of excessively large 4750-4999 1146 0.3 134 12 infants grew during the 20th century. According to Williams 5000-5249 385 0.1 57 15 (1903), at the beginning of the 20th century, the incidence 5250-5499 127 0.04 31
TABLE 44-2. Birthweight Distribution of 354,509 Liveborn Infants at Parkland Hospital between 1988 and 2012 (g) No. % No. /0 500-3999 322,074 90.9 13,365 4 4000-4249 19,106 5.4 1043 5 4250-4499 8391 2.4 573 7 of birthweight > 5000 g was 1 to 2 per 10,000 births. his 5500 or more 0.02 14 24 compares with 16 per 10,000 births at Parland Hospital from 1988 through 2008 and with 11 per 10,000 in the United States in 2010. he influence of increasing maternal obesity rates is overwhelming, and its association with diabetes is well known. Of Parkland mothers with newborns weighing > 5000 g, more than 15 percent were diabetic.
Several terms currently describe pathological fetal overgrowth. he most common ofthese-macrosomia-is defined by birthweights that exceed certain percentiles for a given population. Another commonly used scheme is to deine macrosomia by an empirical birthweight threshold.
Macrosomia is frequently deined based on mathematical distributions of birthweight. Those newborns exceeding the 90th percentile for a given gestational week are usually used as the threshold for macrosomia or large-for-gestational age (LGA) birthweight. For example, the 90th percentile at 39 weeks is 4000 g. If, however, birthweights that are 2 standard deviations above the mean are used, then thresholds lie at the 97th percentile. Thus, substantially larger newborns are considered macrosomic compared with those at the 90th percentile. Specifically, the birthweight threshold at 39 weeks to be macrosomic would be approximately 4500 g for the 97th percentile rather than 4000 g for the 90th percentile.
Newborn weight exceeding 4000 g (8 lb 13 oz) is also a frequently used threshold to deine macrosomia. Others use 4250 g or even 4500 g (10 lb). As shown in Table 44-2, birthweights ::4500 g are uncommon. During a 30-year period at Parkland Hospital, during which there were more than 350,000 singleton births, only 1.4 percent of newborns weighed 4500 g or more. We are of the view that the upper limit of fetal growth, above which growth can be deemed abnormal, is likely two standard deviations above the mean, representing perhaps 3 percent of births. At 40 weeks, such a threshold would correspond to approximately 4500 g. The American College of Obstetricians and Gynecologists (2016a) concludes that the term macrosomia was an appropriate appellation for newborns who weigh 4500 g or more at birth.