Is the angle of needle insertion influencing the created defect in human fetal membranes? Evaluation of the agreement between specialists' opinions and ex vivo observations

OBJECTIVE: We sought to evaluate the agreement between the opinions of spec ialists in fetal medicine with ex vivo observations on the potential influe nce of the angle of needle insertion on the fluid leak through the created defect in human fetal membranes. STUDY DESIGN: Membranes from placentas of women who were delivered by elect ive cesarean were harvested, cut in pieces, and secured to the bottom of pl astic tubes filled with Hartmann solution. They were punctured with 18-, 20 -, or 22-gauge needles, with an angle of insertion of 90 degrees (group 1) or 45 degrees (group 2), and the flow rate (in milliliters per minute) thro ugh the created defect at a constant pressure of 150 mm H2O was measured. F ifty physicians performing amniocentesis at fetal medicine reference center s were interviewed about their impression and clinical attitude with respec t to the angle of needle insertion at the time of amniocentesis. RESULTS: In the ex vivo study puncture with a 45 degrees angle was associat ed with a significantly lower flow of fluid through the membrane defect for all needle sizes tested. Regarding survey answers, 82% of physicians try t o perform amniocentesis with a given angle (ie, 90 degrees in the vast majo rity of cases). Among the reasons for doing so, minimizing membrane damage was mentioned in more than half of cases. CONCLUSION: These results provide evidence that the angle of needle inserti on influences the type of defect and therefore the flow rate through human membranes. Membrane damage is a concern of a proportion of specialists whil e performing amniocentesis, but ex vivo observations do not agree with clin ical assumptions on the potential influence of the angle of insertion.