Aspiration of oocytes for in-vitro fertilization.

An aspiration system, incorporating a regulated vacuum pump, was used to examine, in vitro, some factors that may affect oocyte collection. In an open aspiration system, as the length of the needle was increased, or the internal diameter decreased, the velocity (and flow rate) of aspirated fluid decreased. There was a difference, however, between experimental flows and those predicted by Hagen-Poiseuille's Law. Upon application of vacuum to a closed aspiration system, employing isolated bovine ovaries, there was an initial rapid increase in the collection tube vacuum to 85% of the selected pump vacuum followed by a more gradual rise to 100%. The vacuum within the needle similarly rose rapidly to approximately half the selected vacuum, while the vacuum at the needle tip was approximately 5% of selected vacuum. The vacuums throughout the system briefly equilibrated as maximum flow/velocity was reached. Flow/velocity slowed dramatically as the follicle collapsed, and stopped as the needle tip was blocked. If vacuum was maintained during the withdrawal of the needle from the follicle, there was a dramatic forward flow of fluid toward the collection tube. The morphological appearance of bovine cumulus after in-vitro aspiration was generally unaltered by vacuums commonly utilized in oocyte collection, providing the cumulus was regular, compact and refractile. The cumulus was less resistant to aspiration if it was damaged or had degenerated. These results suggest that an intact cumulus may offer protection during oocyte collection.