Based on gestational age, miscarriages can be classified into early and late miscarriage.
Early miscarriages occur in the very first weeks of pregnancy, approximately until week 12. From this week onwards, they are considered late miscarriages.
As for chemical pregnancy, it is a type of very early miscarriage that occurs after a positive pregnancy test. It is a consequence of early embryonic arrest. The embryo is eliminated with bleeding, which in most cases is confused by menstrual flow.