Spontaneous abortion is categorized as threatened, inevitable, incomplete, complete, or missed.
Spontaneous abortion can be classified further as sporadic or recurrent. Inevitable abortion is defined as bleeding of intrauterine origin with continuous and progressive dilation of the cervix but without expulsion of conception products before the 20th week of gestation. The timing of a spontaneous abortion suggests its pathophysiology. Anatomic factors usually are associated with second-trimester loss. These pregnancies usually are not clinically recognized.