The position of the metaphase II spindle cannot be predicted by the location of the first polar body in the human oocyte

When performing intracytoplasmic sperm injection (ICSI) on human oocytes, t he injection is traditionally made at the 3 o'clock position, with the firs t polar body (PB) at the 12 or 6 o'clock position. This has been based on t he assumption that the second meiotic metaphase II (MII) spindle lies in cl ose proximity to the first PB, The objective of this study mas to document the actual spatial relationship between the first PB and the MII spindle bo th in in-vitro matured (fresh) human MII oocytes and in oocytes matured in vitro. We found that the MII spindle was, on average, not located directly adjacent to the PB, The in-vivo group (n = 54) showed a mean deviation of t he MII spindle from the position of the PB of 41.7 degrees and the in-vitro group 26.6 degrees (n = 43), The difference between the angle of the two g roups was statistically significant (P = 0.005), indicating that the latera l displacement of the first PB is only partly due to the denuding procedure during ICSI, because the in-vitro matured oocytes were denuded before extr usion of the first PB. The majority of the MII spindles in both groups were found in the same hemisphere as the first PB, suggesting that care should be taken to avoid damaging the MII, spindle by inserting the ICSI needle in the other half of the oocyte.