title: Placental plasticity in monochorionic twins: Impact on birth weight and placental weight.
abstract: BACKGROUND
  The knowledge about adaptive mechanisms of monochorionic placentas to fulfill the demands of two instead of one fetus is largely speculative. The aim of our study was to investigate the impact of chorionicity on birth weight and placental weight in twin pregnancies.
  
  
  METHODS
  Forty Monochorionic (MC) and 43 dichorionic (DC) twin pregnancies were included in this retrospective study. Individual and total (sum of both twins) birth weights, placental weights ratios between placental and birth weights and observed-to-expected (O/E)-ratios were calculated and analyzed. Additionally, we investigated whether in twin pregnancies placental and birth weights follow the law of allometric metabolic scaling.
  
  
  RESULTS
  MC pregnancies showed higher placental O/E-ratios than DC ones (2.25 ± 0.85 versus 1.66 ± 0.61; p < 0.05), whereas the total neonatal birth weight O/E-ratios were not different. In DC twins total placental weights correlated significantly with gestational age (r = 0.74, p < 0.001), but not in MC twins. Analysis of deliveries ≤32 weeks revealed that the placenta to birth weight ratio in MC twins was higher than in matched DC twins (0.49 ± 0.3 versus 0.24 ± 0.03; p = 0.03). Allometric metabolic scaling revealed that dichorionic twin placentas scale with birth weight, while the monochorionic ones do not.
  
  
  CONCLUSIONS
  The weight of MC placentas compared to that of DC is not gestational age dependent in the third trimester. Therefore an early accelerated placental growth pattern has to be postulated which leads to an excess placental mass particularly below 32 weeks of gestation. The monochorionic twins do not follow allometric metabolic scaling principle making them more vulnerable to placental compromise.
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, Bern University Hospital, University of Bern, Switzerland.
authors.forename: Marc U
authors.initials: MU
authors.lastname: Baumann
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, Bern University Hospital, University of Bern, Switzerland.
authors.forename: Michelle
authors.initials: M
authors.lastname: Marti
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, Bern University Hospital, University of Bern, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Durrer
authors.affiliation: Computational Science and Engineering Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: Petros
authors.initials: P
authors.lastname: Koumoutsakos
authors.affiliation: Computational Science and Engineering Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Angelikopoulos
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, Bern University Hospital, University of Bern, Switzerland.
authors.forename: Daniele
authors.initials: D
authors.lastname: Bolla
authors.affiliation: Women's Health and Perinatology Research Group, Department of Clinical Medicine, Faculty of Health Sciences, University of Tromsø - The Arctic University of Norway, Tromsø N - 9037, Norway.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Acharya
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, Bern University Hospital, University of Bern, Switzerland.
authors.forename: Ursina
authors.initials: U
authors.lastname: Bichsel
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, Bern University Hospital, University of Bern, Switzerland.
authors.forename: Daniel V
authors.initials: DV
authors.lastname: Surbek
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, Bern University Hospital, University of Bern, Switzerland. Electronic address: luigi.raio@insel.ch.
authors.forename: Luigi
authors.initials: L
authors.lastname: Raio
mesh_terms: D000328:Adult; D001699:Biometry; D001724:Birth Weight; D005260:Female; D006801:Humans; D009929:Organ Size; D010920:Placenta / Q000502:physiology*; D011247:Pregnancy; D059285:Pregnancy, Twin / Q000502:physiology*; D012189:Retrospective Studies; D014430:Twins, Monozygotic; D055815:Young Adult
keywords: Allometric metabolic scaling; Birth weight; Dichorionic; Fetal:placental ratio; Monochorionic; Placental weight; Twin pregnancy