New U/S-based tool for prediction of fetal weight and adverse outcomes

June 21, 2012

Customized estimated fetal weight (EFW) percentiles based on ultrasound (U/S)-derived EFWs better predict adverse perinatal outcomes than older population-based methods, according to an historic cohort study.

Fetal weight derived using customized U/S is a better predictor of adverse outcomes than traditional population-based size measures.

Weights derived at 24 to 28 and 28 to 32 weeks were strongly associated with actual birthweights.

Customized estimated fetal weight (EFW) percentiles based on ultrasound (U/S)-derived EFWs better predict adverse perinatal outcomes than older population-based methods, according to an historic cohort study.

The study, published in the American Journal of Obstetrics and Gynecology, involved 782 women with singleton pregnancies who delivered at a single hospital in Texas at ≥24 weeks’ gestation. The researchers used the most recent U/S obtained during the pregnancy.

During the 1-year study period, the investigators found that the customized method identified 15.1% of small-for-gestational-age (SGA) and 6.8% of large-for-gestational-age (LGA) fetuses, versus 3.8% and 1.7%, respectively, identified by traditional population-based methods.

Of all the fetuses identified as SGA by prenatal U/S, almost half (48.4%) of those identified by the customized EFW percentile method, versus 14.8% identified by the population-based method, were confirmed at birth to be SGA. Similarly, of all the fetuses identified as LGA by prenatal U/S, almost half (44.6%) diagnosed by the customized method, versus 12.5% of those diagnosed with traditional methods, were confirmed at birth to be LGA.

Furthermore, all of the adverse perinatal outcomes considered in the study (ie, preterm birth ≤34 weeks, preterm birth ≤37 weeks, neonatal intensive care unit admission, and cesarean delivery for fetal indications) occurred more frequently in those identified by the customized method than by the population-based method.

The authors claim their study is important because it identifies a link “between prenatal customized EFW <10th percentile and >90th percentile and adverse pregnancy outcomes.” In addition, it demonstrates “a strong association between the customized EFW at 24 to 28 weeks and at 28 to 32 weeks and actual birth weight.”

The authors hope the method proves to be a more accurate way for physicians to determine with certainty which fetuses are abnormal, and in turn, at risk, and which are simply small or large but otherwise healthy. More prospective studies are needed to confirm their findings.

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