title: Placental weight, birth weight and fetal:placental weight ratio in dichorionic and monochorionic twin gestations in function of gestational age, cord insertion type and placental partition.
abstract: BACKGROUND
  We established reference values for placental weight, birth weight, and fetal:placental weight ratio (FPR) (a possible index of placental functional efficiency) in monochorionic and dichorionic twin gestations.
  
  
  METHODS
  Placental weight, birth weight, and FPR in function of gestational age, cord insertion type and placental sharing were determined in 151 dye-injected diamniotic-monochorionic and 198 double-disc diamniotic-dichorionic twin placentas (25-39 weeks' gestation).
  
  
  RESULTS
  As expected, FPR values increased with gestational age in both groups. Birth weights and placental weights of monochorionic twins >28 weeks' gestation were significantly lower than those of age-matched dichorionic twins. When stratified per placental weight, the birth weights and FPR values of monochorionic twins were overall lower than those of dichorionic twins within the same placental weight category. However, in the subset of monochorionic twins with small share in unevenly partitioned placentas, birth weights and FPR values per placental weight were similar to those of dichorionic twins, and significantly higher than those of monochorionic twins with larger share or even placental sharing. Cord insertion type did not correlate with birth weight or FPR values per placental weight in either twin type.
  
  
  CONCLUSIONS
  Reference values were generated for placental weight, birth weight and FPR in monochorionic and double-disc dichorionic twins. The generally lower FPR per placental weight in monochorionic twins compared with dichorionic twins is suggestive of inherently lower placental functional efficiency in monochorionic gestations. The mechanisms and clinical implications of the apparent differential modulation of FPR/efficiency in monochorionic twins according to placental partitioning remain to be determined.
authors.affiliation: The Department of Pathology, Women and Infants Hospital, Providence, RI 02905, USA; The Department of Pathology and Laboratory Medicine, Alpert Medical School of Brown University, Providence, RI 02905, USA; The Program in Fetal Medicine, Alpert Medical School of Brown University, Providence, RI 02905, USA. Electronic address: mdepaepe@wihri.org.
authors.forename: M E
authors.initials: ME
authors.lastname: De Paepe
authors.affiliation: The Department of Pathology, Women and Infants Hospital, Providence, RI 02905, USA.
authors.forename: S
authors.initials: S
authors.lastname: Shapiro
authors.affiliation: The Department of Pathology, Women and Infants Hospital, Providence, RI 02905, USA.
authors.forename: L E
authors.initials: LE
authors.lastname: Young
authors.affiliation: The Program in Fetal Medicine, Alpert Medical School of Brown University, Providence, RI 02905, USA.
authors.forename: F I
authors.initials: FI
authors.lastname: Luks
mesh_terms: D000328:Adult; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D020567:Fetal Weight; D005865:Gestational Age; D006801:Humans; D009929:Organ Size; D010920:Placenta / Q000033:anatomy & histology*; D011247:Pregnancy; D059285:Pregnancy, Twin / Q000502:physiology; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D014470:Umbilical Cord / Q000033:anatomy & histology*
keywords: Anastomoses; Marginal cord; Monochorionic twin; Placenta; Velamentous cord