title: Timing of early amniocentesis as a function of membrane fusion.
abstract: OBJECTIVE
  The purpose of this prospective study was to evaluate sonographically the timing of membrane fusion and to determine its possible effect on the timing of amniocentesis.
  
  
  METHODS
  Between May 18, 1998, and January 31, 2002, the status of amnion fusion in pregnant patients at 9-15 weeks' menstrual age was identified in women who were to undergo obstetric sonography. Amniocentesis was performed if even a small area of fused membranes that could be traversed was identified; if the membranes were completely unfused, amniocentesis was delayed. The effect of membrane fusion in terms of the need to reschedule amniocentesis was evaluated.
  
  
  RESULTS
  We examined a total of 594 patients. Membrane fusion occurred progressively with increasing menstrual age. One hundred six early amniocenteses were scheduled, and 70 were performed; the others were delayed because the membranes were unfused. Our requirement that an area of membrane fusion be found before we would perform amniocentesis resulted in rescheduling the procedure 24-38% of the time.
  
  
  CONCLUSIONS
  Membrane fusion, as seen sonographically, is a function of menstrual age. Even by 15 weeks, a portion of the amnion may be unfused with the chorion. Amniocenteses scheduled for early in the pregnancy may need to be delayed until later, when the membranes are at least partially fused, allowing safe passage of a needle. Delaying the procedure may incur higher expense but may be important in terms of lessening the risk involved.
authors.affiliation: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Maine Medical Center, 887 Congress Street, Suite 200, Portland, Maine 04102, USA.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Pinette
authors.forename: Joseph
authors.initials: J
authors.lastname: Wax
authors.forename: Jacquelyn
authors.initials: J
authors.lastname: Blackstone
authors.forename: Angelina
authors.initials: A
authors.lastname: Cartin
authors.forename: Donald
authors.initials: D
authors.lastname: McCrann
mesh_terms: D000649:Amniocentesis / Q000009:adverse effects*; D000650:Amnion / Q000502:physiology*; D005260:Female; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal