Despite increasing use of ultrasound in obstetrics, the task of accurately identifying fetuses at risk of stillbirth from chronic placental diseases (Kingdom JC, et al. Am. J. Obstet. Gynecol. 2018;218:S803–17) continues to elude us. Using fetal biometry to calculate an estimated fetal weight (EFW) and plotting it on a growth chart is fraught with potential errors. Recent research clarifies that the Hadlock formula using head circumference, abdominal circumference, and femur length to calculate EFW performs best and should therefore be used universally (Hammami A, et al. Vol. 52, Ultrasound Obstet Gynecol. 2018;5:35–43). The next step is to convert the given EFW into a percentile, based on a presumed normal range for a given gestational age. Until relatively recently, clinicians used the distribution of birthweight for a given week of gestation. These charts make an implicit and untrue assumption, namely, that the subset of babies born at a given week are a representative sample of all on-going pregnancies at the same week. While this may be true (or rather, less untrue) at term, it is not true preterm, given the association between placental dysfunction with both spontaneous and medically indicated preterm birth. Use of a birth weight-based chart means many growth-restricted pregnancies will be missed at preterm gestational ages.