This work identifies how age-associated aneuploidy occurs in humans, which can cause infertility, miscarriages, and birth defects. We show that, in eggs from older women, inter-kinetochore distances between sister chromatids increases significantly, indicating weakened cohesion, as do the rates of unpaired sister chromatids. This indicates that loss of cohesion with increased age likely contributes to increases in aneuploidy. Read Article.