Adverse pregnancy outcome and association with small for gestational age birthweight by customized and population-based percentiles

OBJECTIVE: The objective of the study was to investigate the association between pregnancy complications and small for gestational age (SGA) birthweight, comparing SGA based on the customized growth potential with SGA based on the birthweight standard of the same population. STUDY DESIGN: This was a retrospective analysis of a database from a US multicenter study. Pregnancy complications included threatened preterm labor, antepartum hemorrhage, pregnancy-induced hypertension, preeclampsia, stillbirth, and early neonatal death. RESULTS: Compared with SGA by the birthweight standard, SGA by customized growth potential showed higher risk for each of the 6 adverse indicators. A third of the SGA group was small by customized centiles but not by population- based centiles, yet was strongly associated with each of the pregnancy complications studied. This subgroup of unrecognized SGA babies included 26% preterm deliveries. In contrast, a subgroup that was SGA by the population standard but not by the customized standard (17.2%), was not associated with any of the indicators of adverse outcome. CONCLUSION: SGA defined by customized growth potential improves the differentiation between physiologically and pathologically small babies.