I just had ER for my first IVF. 20 eggs were retrieved: 4 didn't fertilize, 2 were single-PN, 3 were polyspermic, and 11 seemed to fertilize normally. There are several in the 11 batch that have vacuoles in them. The nurse described these as bubbles in the egg, and said it could point to an egg quality issue.
What exactly are vacuoles and what causes them? Do the vacuoles mean the eggs/embroys are not viable?
Also, for the single-PN and polyspermic, are these common?
Cytoplasmic vacuoles (small fluid-filled sacs) are caused when the eggs or embryonic cells are in the process of regulating the amount of water inside the cell. If too much water is getting into the cell through the plasma membrane, the cell forms vacuoles to "export" the extra water. These vacuoles migrate to the cell surface and discharge their contents to the outside of the cell. A small number of vacuoles is usually a transitory observation and of no great concern. A large number of vacuoles can indicate that the plasma membrane of the egg or embryonic cell is leaky and is letting too much water get inside the cell. This is more serious and can indicate an "egg problem". So, its really a matter of degree.
Under ordinary conditions, about 17 hours after insemination, two pronuclei are clearly visable in the egg cytoplasm. One pronuclei is from the sperm and one is from the egg. Each pronuclei contains one half of the chromosomes. They migrate together, fuse and form the nucleus of the 1-celled embryo (zygote). Somtimes a sperm gets inside, but the egg is a dud. The sperm pronucleus forms, but the egg's does not. Conversly, the sperm may not form a pronucleus and the egg does, In either case, the embryologist sees only one pronucleus. These eggs/embryos are considered genetically abnormal and are discarded. When more than one sperm gets inside, three or more pronuclei can form. These are also genetically abnormal and are discared. Abnormalities of pronuclear development (1PN or 3+PN) are often due to inadequate maturity of the egg cytoplasm (i.e. the egg came from a small immature follicle). It is not that unsual, so I wouldn't be overly concerned.
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