Fetal Weight Estimation at 31 Weeks Gestation

Reference Values

• The Society for Maternal-Fetal Medicine provides specific weight estimates at 31 weeks gestation, with a mean estimated fetal weight of approximately 1500g (approximately 3.3 pounds) 1
• The average estimated fetal weight at 31 weeks gestation is approximately 1500 grams, ranging from 1400-1700g depending on the reference standard used, according to the American Journal of Obstetrics and Gynecology 1, 2

Clinical Assessment

• The American College of Obstetricians and Gynecologists defines abnormal growth as an estimated fetal weight below the 10th percentile for gestational age, which would correspond to weights below approximately 1300g at 31 weeks 3, 4
• Severe fetal growth restriction is defined as estimated fetal weight below the 3rd percentile, carrying significantly increased risk of adverse perinatal outcomes regardless of Doppler findings 3, 4

Important Clinical Considerations

• Accurate pregnancy dating using first-trimester crown-rump length is essential for interpreting fetal weight at any gestational age, as misdating can lead to misclassification of growth abnormalities 3, 4
• The American College of Obstetricians and Gynecologists recommends using population-based references rather than customized standards when determining fetal weight percentiles 3