BACKGROUND AND PURPOSE:

• RCOG and ACOG have differing definitions of fetal growth restriction
  • RCOG: Estimated fetal weight <10th percentile or abdominal circumference <10th percentile
  • ACOG: Estimated fetal weight <10th percentile
• Blue et al. (Obstetrics & Gynecology, 2018) compared the efficacy of these two methods of predicting small for gestational age (SGA) birth

METHODS:

• Retrospective Review (2013-2017)
• Included mothers with singleton, well-dated pregnancies and noanomalous fetuses
  • Indicated fetal growth restriction surveillance
  • Ultrasound-estimated fetal weight within 30 days of delivery
  • Hadlock intrauterine growth curve
• Small for gestational age (SGA): Birth weight <10^th percentile based on a recent, sex-specific curve
• Area under the curve (AUC), sensitivity, specificity, and positive and negative likelihood ratios were calculated
• DeLong analysis used to determine significance, rather than overlapping CIs

RESULTS:

• 1,704 pregnancies were included
  • 235 (13.8%) of pregnancies results in SGA
• Rate of fetal growth restriction differed between the two guidelines (P=.007)
  • ACOG: 13.6%
  • RCOG: 16.9%
• RCOG’s diagnostic approach had a significantly higher area under the curve (P=.01)
  • RCOG: 0.78 (95% CI 0.76–0.80)
  • ACOG: 0.76 (95% CI 0.74–0.78)
• Sensitivities and specificities of the various methods were similar
• Adopting estimated fetal weight or abdominal circumference less than the 10th percentile instead of estimated fetal weight alone to predict SGA at birth would correctly identify one additional case of SGA for each 14 patients assessed

CONCLUSION:

• The guidelines introduced by RCOG are better in predicting SGA, although not by a large margin
• Benefit of better prediction is the identification of fetuses at risk for stillbirth
• This study does not address outcomes and would require a larger, prospective study, including determining whether newborns are truly smaller than their potential or are simply constitutionally small

Learn More – Primary Sources:

A Comparison of Methods for the Diagnosis of Fetal Growth Restriction Between the Royal College of Obstetricians and Gynaecologists and the American College of Obstetricians and Gynecologists

Related ObG Topics:

Can Abdominal Circumference Alone Be Used to Predict SGA or LGA Newborns?

Can Artery Doppler Studies Predict Small for Gestational Age Neonates?

Is There an Association Between High or Low Weight Gain and Maternal and Infant Outcomes?