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. Age and increased parity affect the risk of a miscarriage.
Age primarily affects the oocyte.
When oocytes from young women are used to create embryos for transfer to older recipients, implantation and pregnancy rates mimic those seen in younger women, and the number of miscarriages and chromosomal anomalies decreases. This phenomenon suggests that the uterus is not responsible for poor outcomes in women of advanced reproductive age. Bleeding may be roughly quantified by the number of pads soaked per hour or day. An average pad absorbs approximately 20-30 mL of blood. Preexisting anemia may make a patient more susceptible to hypovolemic shock.