The objective of this study was to compare the frequency of abnormal fetal growth in women with diabetes mellitus (DM) using population-based birth weight (pop BW) percentiles compared with customized birth weight (cust BW) percentiles, which include adjustments for maternal race, parity, height, weight, and fetal sex. The study design comprised a retrospective cohort of singleton DM pregnancies delivered over a 1-year period (June 2007 to May 2008) from a single tertiary care university-based medical center. Inclusion criteria were gestational age >20 weeks at delivery, live birth, and absence of major chromosomal/structural abnormalities. Small for gestational age (SGA), <10th percentile, and large for gestational age (LGA), >90th percentile pregnancies were categorized based on pop BW or cust BW standards. There were significant differences in the rates of SGA (p < 0.004) and LGA (p < 0.001) between cust BW and pop BW methods. When comparing the two methods, pop BW did not identify 13/16 (81%) of SGA and 23/39 (59%) of LGA babies defined by cust BW methods. The use of cust BW calculation in a diabetic population identified a greater percentage of neonates with pathologic fetal growth compared with pop BW standards, suggesting that the population standard may underdiagnose abnormal fetal growth in diabetic pregnancies.
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