Approaches to oocyte retrieval for advanced reproductive technology cycles planning to utilize in vitro maturation: a review of the many choices to be made.

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To evaluate the minutiae associated with oocyte retrieval for use in human in vitro maturation IVF cycles. Many of the relevant features of oocyte retrieval were identified by the Trounson group in the first publication on successful in vitro maturation using transvaginal oocyte harvesting and these were a major focus of this review. Published human and animal studies, together with topics from mathematics and mechanics, were used to try to understand the importance of different choices that could be made in structuring a transvaginal oocyte retrieval procedure in humans. The published literature suggests that the highest oocyte recovery rate occurs using higher pressures and thicker needles, but this comes at the cost of damaging the cumulus oocyte complex. It is likely that this damage is caused by the sheer stress forces exerted on the cumulus oocyte complex due to parabolic forces associated with laminar flow within the needle and is likely worsened by irregular forces during intervals of turbulent flow occurring with entry into the needle. Larger needles also cause more pain and may be associated with more blood loss. Higher velocity entry into the follicle, needle rotation to prevent premature blockage of the lumen, and carefully timed applications of aspiration pressure theoretically optimize oocyte retrieval technique. Oocyte retrieval for in vitro maturation is effected by the interaction of the many choices that need to be made in planning for the procedure. The most difficult decision involves aspiration pressure or fluid flow rate and needle size.