title: Estimation of Fetal Weight during Labor: Still a Challenge.
abstract: OBJECTIVE
  To evaluate the accuracy of fetal weight prediction by ultrasonography labor employing a formula including the linear measurements of femur length (FL) and mid-thigh soft-tissue thickness (STT).
  
  
  METHODS
  We conducted a prospective study involving singleton uncomplicated term pregnancies within 48 hours of delivery. Only pregnancies with a cephalic fetus admitted in the labor ward for elective cesarean section, induction of labor or spontaneous labor were included. We excluded all non-Caucasian women, the ones previously diagnosed with gestational diabetes and the ones with evidence of ruptured membranes. Fetal weight estimates were calculated using a previously proposed formula [estimated fetal weight = 1687.47 + (54.1 x FL) + (76.68 x STT). The relationship between actual birth weight and estimated fetal weight was analyzed using Pearson's correlation. The formula's performance was assessed by calculating the signed and absolute errors. Mean weight difference and signed percentage error were calculated for birth weight divided into three subgroups: < 3000 g; 3000-4000 g; and > 4000 g.
  
  
  RESULTS
  We included for analysis 145 cases and found a significant, yet low, linear relationship between birth weight and estimated fetal weight (p < 0.001; R2 = 0.197) with an absolute mean error of 10.6%. The lowest mean percentage error (0.3%) corresponded to the subgroup with birth weight between 3000 g and 4000 g.
  
  
  CONCLUSIONS
  This study demonstrates a poor correlation between actual birth weight and the estimated fetal weight using a formula based on femur length and mid-thigh soft-tissue thickness, both linear parameters. Although avoidance of circumferential ultrasound measurements might prove to be beneficial, it is still yet to be found a fetal estimation formula that can be both accurate and simple to perform.
authors.affiliation: Hospital Universitário de Santa Maria, Centro Hospitalar Lisboa Norte, Lisboa, Portugal.
authors.forename: Joana Goulão
authors.initials: JG
authors.lastname: Barros
authors.affiliation: Hospital Universitário de Santa Maria, Centro Hospitalar Lisboa Norte, Lisboa, Portugal.
authors.forename: Inês
authors.initials: I
authors.lastname: Reis
authors.affiliation: Hospital Universitário de Santa Maria, Centro Hospitalar Lisboa Norte, Lisboa, Portugal.
authors.forename: Isabel
authors.initials: I
authors.lastname: Pereira
authors.affiliation: Hospital Universitário de Santa Maria, Centro Hospitalar Lisboa Norte, Lisboa, Portugal.
authors.forename: Nuno
authors.initials: N
authors.lastname: Clode
authors.affiliation: Hospital Universitário de Santa Maria, Centro Hospitalar Lisboa Norte, Lisboa, Portugal.
authors.forename: Luís M
authors.initials: LM
authors.lastname: Graça
mesh_terms: D001724:Birth Weight; D005260:Female; D020567:Fetal Weight; D006801:Humans; D007231:Infant, Newborn; D007743:Labor, Obstetric; D011247:Pregnancy; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal
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