title: In-vivo stretch of term human fetal membranes.
abstract: BACKGROUND
  Fetal membranes (FM) usually fail prior to delivery during term labor, but occasionally fail at preterm gestation, precipitating preterm birth. To understand the FM biomechanical properties underlying these events, study of the baseline in-vivo stretch experienced by the FM is required. This study's objective was to utilize high resolution MRI imaging to determine in-vivo FM stretch.
  
  
  METHODS
  Eight pregnant women (38.4 ± 0.4wks) underwent abdominal-pelvic MRI prior to (2.88 ± 0.83d) caesarean delivery. Software was utilized to determine the total FM in-vivo surface area (SA) and that of its components: placental disc and reflected FM. At delivery, the SA of the disc and FM in the relaxed state were measured. In-vivo (stretched) to delivered SA ratios were calculated. FM fragments were then biaxially stretched to determine the force required to re-stretch the FM back to in-vivo SA.
  
  
  RESULTS
  Total FM SA, in-vivo vs delivered, was 2135.51 ± 108.47 cm(2) vs 842.59 ± 35.86 cm(2); reflected FM was 1778.42 ± 107.39 cm(2) vs 545.41 ± 22.90 cm(2), and disc was 357.10 ± 28.08 cm(2) vs 297.18 ± 22.14 cm(2). The ratio (in-vivo to in-vitro SA) of reflected FM was 3.26 ± 0.11 and disc was 1.22 ± 0.10. Reflected FM re-stretched to in-vivo SA generated a tension of 72.26 N/m, corresponding to approximate pressure of 15.4 mmHg. FM rupture occurred at 295.08 ± 31.73 N/m corresponding to approximate pressure of 34 mmHg. Physiological SA was 70% of that at rupture.
  
  
  CONCLUSIONS
  FM are significantly distended in-vivo. FM collagen fibers were rapidly recruited once loaded and functioned near the failure state during in-vitro testing, suggesting that, in-vivo, minimal additional (beyond physiological) stretch may facilitate rapid, catastrophic failure.
authors.affiliation: Department of Bioengineering, Swanson School of Engineering, School of Medicine, University of Pittsburgh, Pittsburgh PA, USA.
authors.forename: E M
authors.initials: EM
authors.lastname: Joyce
authors.affiliation: Department of Radiology, MetroHealth Medical Center and Case Western Reserve University, USA; Department of Biomedical Engineering, Case Western Reserve University, USA.
authors.forename: P
authors.initials: P
authors.lastname: Diaz
authors.affiliation: Department of Radiology, MetroHealth Medical Center and Case Western Reserve University, USA.
authors.forename: S
authors.initials: S
authors.lastname: Tamarkin
authors.affiliation: Department of Pediatrics, MetroHealth Medical Center and Case Western Reserve University, USA.
authors.forename: R
authors.initials: R
authors.lastname: Moore
authors.affiliation: Department of Pediatrics, MetroHealth Medical Center and Case Western Reserve University, USA.
authors.forename: A
authors.initials: A
authors.lastname: Strohl
authors.affiliation: Department of Reproductive Biology, MetroHealth Medical Center and Case Western Reserve University, Cleveland, OH, USA.
authors.forename: B
authors.initials: B
authors.lastname: Stetzer
authors.affiliation: Department of Pediatrics, MetroHealth Medical Center and Case Western Reserve University, USA.
authors.forename: D
authors.initials: D
authors.lastname: Kumar
authors.affiliation: Department of Biomedical Engineering and the Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, TX 78712-0027, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Sacks
authors.affiliation: Department of Pediatrics, MetroHealth Medical Center and Case Western Reserve University, USA; Department of Reproductive Biology, MetroHealth Medical Center and Case Western Reserve University, Cleveland, OH, USA. Electronic address: jmoore@metrohealth.org.
authors.forename: J J
authors.initials: JJ
authors.lastname: Moore
mesh_terms: D001696:Biomechanical Phenomena; D005321:Extraembryonic Membranes / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D005322:Premature Rupture of Fetal Membranes / Q000000981:diagnostic imaging / Q000469:parasitology / Q000503:physiopathology; D005865:Gestational Age; D006801:Humans; D007743:Labor, Obstetric; D008279:Magnetic Resonance Imaging; D011247:Pregnancy; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology*; D047929:Term Birth
keywords: Biomechanics; Deformation; Fetal membranes; Intrauterine stretch; MRI; Surface area