But the ethical and practical implications of keeping potential humans on ice are now becoming abundantly clear. Increasingly, divorced couples fight over frozen embryos. And the preservation of genetic material – embryos, eggs, and sperm -- created by biological parents who may be well beyond their reproductive years gives others pause. In 2007, a mother froze eggs for use by her daughter, then seven years old, who was born with a condition that could make her infertile. If the daughter someday uses the embryos, she will give birth to her half-brother or half-sister.