The process of freezing a woman's eggs so that they can be used at a future time is a new technology. Once a woman is ready to have a baby, the eggs can be thawed and fertilized (merging sperm with an egg to form a new human being). Eggs and sperm contain the hereditary material, or DNA (deoxyribonucleic acid), of the parents. In vitro fertilization is a process that combines a woman's egg with a man's sperm in a laboratory to form an embryo (a multicelled fertilized egg). The embryo can then be implanted in the woman's uterus where it continues to develop into a baby.
Doctors have been able to freeze embryos for many years. In vitro fertilization often results in too many embryos. The extra embryos may be frozen until the woman is ready to get pregnant, but many stay frozen for years because the parents do not use them. Keeping embryos frozen is controversial because some people believe embryos are human lives. Freezing only the eggs provides another option.
In order to collect eggs from a woman, she is given specific hormones (chemicals in the body that control the actions of cells and organs) that make her ovaries produce more eggs than normal. A doctor then surgically removes the eggs from the woman's ovary using a small needle.
The eggs must be protected during the freezing process so they are not damaged. One way to do this is by adding chemicals to the eggs. The chemicals replace the water in the eggs to prevent ice crystals from forming when the eggs are frozen. Another method is to freeze them so quickly that ice crystals do not have a chance to form.
When a woman is ready to get pregnant, doctors thaw one or more eggs using special chemicals. The eggs and sperm are combined in a lab. If they make an embryo, the doctor places it in the woman's uterus to grow.
Frozen eggs could also play an important part in preserving endangered animals. The Frozen Zoo, affiliated with the San Diego Zoo, collects and maintains frozen eggs, sperm, embryos, DNA, and tissue samples of animals whose numbers are dwindling in the wild. Scientists hope to ensure the survival of endangered species by learning efficient techniques to assist their reproduction.
