Methods
The study population was drawn from patients undergoing IVF/ICSI cycles in our program at Brigham and Women's Hospital from March 2011 to April 2012. Oocytes from only one cycle for each patient were included in the study. Cycles with at least two germinal vesicle stage oocytes were included with random allocation of one oocyte to culture for 30 h without BPA and remaining sibling oocytes to medium-containing BPA (20, 200 ng/ml or 20 µg/ml). Oocytes were fixed and labeled for tubulin, actin and chromatin and examined with immunofluorescence and confocal microscopy. Oocytes were assessed for meiotic stage (n = 292), and those at metaphase II (MII, n = 175) were further classified according to their spindle configurations and patterns of chromosome alignment. McNemar's test was used to compare dichotomized maturation status. Generalized estimating equations were used to account for the correlation between oocytes from the same woman and for the spindle analysis. Main