First, let's discuss what embryonic arrest means. There are two scenarios of embryonic arrest. The first scenario is where the embryo initially does not develop well, leading to the cessation of development in the very early stages of pregnancy. The second scenario occurs when the embryo initially develops well, but after a period, embryonic arrest happens. Therefore, embryonic arrest generally occurs during early pregnancy but can also occur later, around the middle of early pregnancy. It can happen at any time, but it is most commonly identified after 8 weeks. However, some cases involve the presence of an embryonic bud and heart tube, and embryonic arrest can still occur even at 10 or 11 weeks.