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220: Neonatal morbidity is increased with the inaccurate diagnosis of fetal growth restriction

      Objective

      With the limited accuracy of fetal growth ultrasound, sonographic screening for fetal growth restriction (FGR) introduces the potential for misdiagnosis of an appropriate-for-gestational age (AGA) fetus as FGR, which may increase the likelihood of iatrogenic prematurity and associated perinatal complications. We sought to determine the frequency of misdiagnosis of FGR in newborns with AGA birth weights, and to test the hypothesis that misdiagnosis of FGR increases the likelihood of prematurity and adverse perinatal outcomes.

      Study Design

      In this retrospective cohort study, the exposed cohort consisted of all singleton, liveborn, non-anomalous infants delivered at Magee-Womens Hospital from 2003-2009 that were AGA at birth, but characterized as FGR on antenatal ultrasound. For each exposed infant, we selected 9 unexposed controls whose birth weight percentile fell within 3 points of the exposed infant and were considered AGA on growth ultrasound during the same gestational week that the exposed infant was considered FGR. Consistent with institutional protocol, fetal and neonatal weights were evaluated using the growth standard published by Fenton. We compared outcomes in exposed and unexposed infants using chi-square test and logistic regression, adjusting for education, tobacco use, marital status, race, and nulliparity.

      Results

      Out of 40,577 AGA newborns that met inclusion criteria, 10,549 (26.0%) underwent fetal growth ultrasound beyond 24 weeks. Of these, only 78 (0.7%) were misdiagnosed as FGR. AGA neonates identified as FGR on ultrasound were more likely to deliver preterm, and more likely to require NICU admission (Table). There was only 1 neonatal death in the entire study cohort, and no cases of 5 min. Apgar<4. Misdiagnosis of FGR was not associated with an increased risk of Cesarean delivery.

      Conclusion

      With use of the Fenton nomogram, the antenatal diagnosis of FGR in AGA neonates was rare, but associated with an increased likelihood of preterm delivery and NICU admission. These risks must be considered when evaluating the utility of fetal growth ultrasound or adoption of less stringent fetal growth standards.
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