Abstract
OBJECTIVE: To compare fetal/infant mortality risk associated with each additional week of expectant management with the infant mortality risk of immediate delivery in growth-restricted pregnancies. METHODS: A retrospective cohort study was conducted of singleton, nonanomalous pregnancies from the 2005-2008 California Birth Registry comparing pregnancies affected and unaffected by growth restriction, defined using birth weights as a proxy for fetal growth restriction (FGR). Birth weights were subdivided as greater than the 90th percentile, between the 10th percentile and 90th percentile, and less than the 10th percentile. Cases greater than the 90th percentile were excluded from analysis. Cases less than the 10th percentile were considered to have FGR and were further subcategorized into <10th percentile, <5th percentile, and <3rd percentile. We compared the risk of infant death at each gestational age week against a composite risk representing the mortality risk of one additional week of expectant management. RESULTS: We identified 1,641,000 births, of which 110,748 (6.7%) were less than 10th percentile. The risk of stillbirth increased with gestational age with the risk of stillbirth at each week of gestation inversely proportional to growth percentile. The risks of fetal and infant mortality with expectant management outweighed the risk of infant death for all FGR categories analyzed beginning at 38 weeks. However, the absolute risks differed by growth percentiles, with the highest risks of infant death and stillbirth in the <3rd percentile cohort. At 39 weeks, absolute risks were low, although the number needed to deliver to prevent 1 death ranged from 413 for <3rd percentile to 2667 in unaffected pregnancies. CONCLUSION: At 38 weeks, the mortality risk of expectant management for one additional week exceeds the risk of delivery across all growth-restricted cohorts, despite variation in absolute risk by degree of growth restriction.