Approximately one-third of medically indicated late preterm births are complicated by fetal growth restriction.

Objective: The purpose of this study was to report the frequency of fetal growth restriction (FGR) based on indication for late preterm birth (LPTB).
Study Design: Singleton live born pregnancies that were delivered from 34-36 weeks 6 days of gestation over a 1-year period at a tertiary care medical center were studied. Indications for delivery were categorized as spontaneous (spontaneous preterm birth or premature rupture of membranes), medically indicated, or elective. A customized birthweight percentile was calculated for each pregnancy; the rate of FGR was compared based on indication for LPTB.
Results: There were 482 LPTBs that met all criteria. Customized birthweight percentiles (median; interquartile range) were different among groups (spontaneous, 45.5%; 20.8-73.5%; medically indicated, 26.9%; 4.1-63.6%; elective, 45.9%; 22.2-78.3%; P = .001). The rate of FGR was also different among groups (spontaneous, 13%; medically indicated, 32%; elective, 21%; P = .001).
Conclusion: With the use of customized birthweight standards, we found that FGR complicated approximately one-third of all cases of medically indicated LPTB.
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