title: Factors influencing the accuracy of fetal weight estimation with a focus on preterm birth at the limit of viability: a systematic literature review.
abstract: BACKGROUND
  Fetal weight estimation (FWE) is an important factor for clinical management decisions, especially in imminent preterm birth at the limit of viability between 23(0/7) and 26(0/7) weeks of gestation. It is crucial to detect and eliminate factors that have a negative impact on the accuracy of FWE.
  
  
  METHODS
  In this systematic literature review, we investigated 14 factors that may influence the accuracy of FWE, in particular in preterm neonates born at the limit of viability.
  
  
  RESULTS
  We found that gestational age, maternal body mass index, amniotic fluid index and ruptured membranes, presentation of the fetus, location of the placenta and the presence of multiple fetuses do not seem to have an impact on FWE accuracy. The influence of the examiner's grade of experience and that of fetal gender were discussed controversially. Fetal weight, time interval between estimation and delivery and the use of different formulas seem to have an evident effect on FWE accuracy. No results were obtained on the impact of active labor.
  
  
  CONCLUSIONS
  This review reveals that only few studies investigated factors possibly influencing the accuracy of FWE in preterm neonates at the limit of viability. Further research in this specific age group on potential confounding factors is needed.
authors.affiliation: Department of Obstetrics and Gynaecology, Bern University Hospital, Bern, Switzerland.
authors.forename: Chantal
authors.initials: C
authors.lastname: Huber
authors.forename: Jarmila A
authors.initials: JA
authors.lastname: Zdanowicz
authors.forename: Martin
authors.initials: M
authors.lastname: Mueller
authors.forename: Daniel
authors.initials: D
authors.lastname: Surbek
mesh_terms: D015992:Body Mass Index; D005328:Fetal Viability / Q000502:physiology*; D020567:Fetal Weight / Q000502:physiology*; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008429:Maternal Welfare; D047928:Premature Birth / Q000175:diagnosis* / Q000503:physiopathology; D012737:Sex Factors