Chorioamniotic membrane separation over the cervical os ("moon sign") in twin-twin transfusion syndrome

J Ultrasound Med. 2014 Jul;33(7):1147-54. doi: 10.7863/ultra.33.7.1147.


Objectives: 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.

Keywords: chorioamniotic membrane separation; endovaginal sonography; moon sign; obstetric ultrasound; rupture of membranes; twin-twin transfusion syndrome.

MeSH terms

  • Adolescent
  • Adult
  • Amnion / diagnostic imaging*
  • Chorion / diagnostic imaging*
  • Female
  • Fetal Growth Retardation / diagnostic imaging
  • Fetal Membranes, Premature Rupture / diagnostic imaging*
  • Fetal Membranes, Premature Rupture / epidemiology
  • Fetofetal Transfusion / diagnostic imaging
  • Fetofetal Transfusion / surgery*
  • Fetoscopy
  • Humans
  • Middle Aged
  • Pregnancy
  • Retrospective Studies
  • Risk Assessment
  • Ultrasonography, Prenatal*
  • Young Adult