Can a sac or yolk grow with dead fetus inside?

In some cases, yes. A sac or yolk can continue to grow with a dead fetus inside, a condition known as a missed abortion or blighted ovum. In such cases, the embryo or fetus stops developing, but the gestational sac or yolk sac may continue to grow for some time. However, it's important to note that the growth is abnormal and will eventually stop. The body may eventually naturally expel the nonviable pregnancy tissue, or medical intervention may be necessary to remove it.