title: Reference weights for placentas delivered before the 28th week of gestation.
abstract: BACKGROUND
  Very few studies have measured the weight of large numbers of placentas delivered before the 28th post-menstrual week.
  
  
  METHODS
  We measured the weight of 930 singleton placentas delivered before the 28th post-menstrual week, and examined the distributions of weights in selected groups (week of gestation, reason for preterm birth, birth weight Z-score categories, placenta histology). We excluded 90 singleton placentas based on growth restriction as indicated by birth weight Z-score, resulting in a normative sample of 840 placentas. Weights for unfused twin placentas are also presented.
  
  
  RESULTS
  Standard weights derived from our data set differ from those previously published, partly due to a larger sample size. Placenta weight varied with birth weight. Placentas from pregnancies ending due to preeclampsia, fetal indications or those showing evidence of poor perfusion on histology were among the smallest and their weights correlated with the smallest birth weights for gestational age.
  
  
  CONCLUSIONS
  Placenta weights appear to be influenced by multiple maternal and fetal processes. We present a standard weight table for singleton placentas among live infants born between 23 and 27 completed weeks.
authors.affiliation: Beth Israel Deaconess Medical Center, Department of Pathology, 330 Brookline Avenue, Boston, MA 02215, USA. jlhecht@bidmc.harvard.edu
authors.forename: J L
authors.initials: JL
authors.lastname: Hecht
authors.forename: H J
authors.initials: HJ
authors.lastname: Kliman
authors.forename: E N
authors.initials: EN
authors.lastname: Allred
authors.forename: S M
authors.initials: SM
authors.lastname: Pflueger
authors.forename: C-H
authors.initials: CH
authors.lastname: Chang
authors.forename: B J
authors.initials: BJ
authors.lastname: Doss
authors.forename: D
authors.initials: D
authors.lastname: Roberts
authors.forename: C A
authors.initials: CA
authors.lastname: Livasy
authors.forename: I
authors.initials: I
authors.lastname: Bhan
authors.forename: E
authors.initials: E
authors.lastname: Zambrano
authors.forename: D W
authors.initials: DW
authors.lastname: Ross
authors.forename: P
authors.initials: P
authors.lastname: Senagore
authors.forename: A N
authors.initials: AN
authors.lastname: Husain
authors.forename: A
authors.initials: A
authors.lastname: Leviton
mesh_terms: D001724:Birth Weight; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D009929:Organ Size; D010920:Placenta / Q000033:anatomy & histology*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000502:physiology*; D011272:Pregnancy, Multiple; D012016:Reference Values; D014427:Twins