title: Chorioamniotic membrane separation over the cervical os ("moon sign") in twin-twin transfusion syndrome.
abstract: OBJECTIVE
  To determine whether chorioamniotic membrane separation from the internal cervical os, the "moon sign," is associated with preterm premature rupture of membranes (PPROM) in twin-twin transfusion syndrome (TTTS).
  
  
  METHODS
  A retrospective study of patients with TTTS treated with laser surgery was performed. Membrane separation before and after surgery was tested against any PPROM, PPROM within 7 days, and PPROM within 21 days. Because intrauterine fetal demise (IUFD) was weakly associated with PPROM, these cases were studied separately.
  
  
  RESULTS
  Among 304 consecutive patients, 247 patients (81.3%) had no IUFD, and preoperative and postoperative membrane separation rates were 13.4% and 13.0%, respectively. In 7 cases (2.8%), preoperative membrane separation disappeared postoperatively, and in 6 cases (2.4%), membrane separation appeared postoperatively; 26 cases (10.5%) had membrane separation at both times. Rates of PPROM did not differ between those who did and did not have preoperative membrane separation (30.3% versus 28.0%; P= .9511). Among those with and without postoperative membrane separation, the rates of any PPROM were 34.4% and 27.4%, respectively (P = .5473), and the rates of PPROM within 21 days were 15.6% and 5.6% (P = .0524). Those with postoperative membrane separation were 3 times more likely to have PPROM within 21 days (odds ratio, 3.13; 95% confidence interval, 1.02-9.58; P= .0453). Preterm premature rupture of membranes was not associated with preoperative or postoperative membrane separation in patients with IUFD.
  
  
  CONCLUSIONS
  The preoperative moon sign does not appear to be associated with PPROM in TTTS. Postoperatively, membrane separation may be weakly associated with PPROM at 21 days, but further research is required to confirm this association.
authors: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California USA.
authors: Shivani
authors: S
authors: Patel
authors: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California USA.
authors: Lisa M
authors: LM
authors: Korst
authors: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California USA.
authors: Arlyn
authors: A
authors: Llanes
authors: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California USA.
authors: Richard H
authors: RH
authors: Lee
authors: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California USA.
authors: Joseph G
authors: JG
authors: Ouzounian
authors: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California USA. chmait@usc.edu.
authors: Ramen H
authors: RH
authors: Chmait
mesh_terms: D000293:Adolescent; D000328:Adult; D000650:Amnion / Q000000981:diagnostic imaging*; D002823:Chorion / Q000000981:diagnostic imaging*; D005260:Female; D005317:Fetal Growth Retardation / Q000000981:diagnostic imaging; D005322:Premature Rupture of Fetal Membranes / Q000000981:diagnostic imaging* / Q000453:epidemiology; D005330:Fetofetal Transfusion / Q000000981:diagnostic imaging / Q000601:surgery*; D005332:Fetoscopy; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D012189:Retrospective Studies; D018570:Risk Assessment; D016216:Ultrasonography, Prenatal; D055815:Young Adult
keywords: chorioamniotic membrane separation; endovaginal sonography; moon sign; obstetric ultrasound; rupture of membranes; twin-twin transfusion syndrome