Morphological analysis identifies five categories of porcine first polar bodies.
Grade 1: Round or ovoid PB1 with intact smooth membrane (A). Grade 2: Round or ovoid PB1 with intact membrane (B). Grade 3: Broken PB1 with a small PB1 fragment (C). Grade 4: Broken PB1 with a big PB1 fragment (D). Grade 5: Broken PB1 completely (E). Grade 1, 2 were considered as good quality. Black arrows: Polar bodies. White arrows: Fragments.