Monozygotic twinning associated with mechanical assisted hatching

Objective: To determine the effect of mechanical assisted hatching on the pregnancy rate (PR). Design: A retrospective comparative analysis of hatched versus nonhatched consecutive assisted reproductive technology (ART) cycles. Setting: A hospital-based ART program. Patient(s): Patients undergoing ART treatment with assisted hatching (1994-1996) were compared with patients who did not have assisted hatching (1990-1993). Intervention(s): None. Main Outcome Measure(s): Pregnancy rate, multiple PR, and rate of monozygotic twinning. Result(s): With hatching, the clinical PR per ET increased from 25.2% to 37.1% and the multiple PR per ET increased from 6.8% to 13.1%. In the nonhatched series, there were no monozygotic twins compared with eight cases in the hatched series (1.2% per ET). Conclusion(s): Mechanical assisted hatching increases the PR but concomitantly elevates the rate of multiple gestation and multiple gestation of high order. There is a particularly high risk of monozygotic twinning with mechanical hatching. (C) 1998 by American Society for Reproductive Medicine.