There are two parts of an egg that are involved in an egg’s maturity. The nuclear component refers to its DNA, and the cytoplasmic component involves the fluid inside the egg (cytoplasm). An egg that is an “M2” is showing a polar body, and its DNA is in a configuration where it can accept the DNA of the sperm. However, the cytoplasm, which contains a variety of factors needed for fertilization/embryo development, may not yet be competent despite the egg being an M2. Larger follicles may produce eggs that have both nuclear and cytoplasmic maturity.
