Pregnancy sac, no embryo bud. What's going on?

Pregnancy sac generally appears in pregnancy 30-40 days, embryo bud will appear in the pregnancy sac about 10 days, there is no embryo, first may be a shorter pregnancy days, if the pregnancy sac has appeared more than 10 days, there is no embryo bud, may be fetal arrest. Progestin and hcg can be done.