A threatened abortion is a condition that occurs during pregnancy and is characterized by vaginal bleeding that does not meet the diagnostic criteria for spontaneous abortion. The cervical os remains closed in a threatened abortion, and it can present during early pregnancy with lower abdominal pain and/or vaginal bleeding. The World Health Organization (WHO) defines a threatened abortion as pregnancy-related bloody vaginal discharge or frank bleeding during the first half of pregnancy without cervical dilatation. A threatened abortion is defined as vaginal bleeding before 20 weeks gestational age in the setting of a positive urine and/or blood pregnancy test with a closed cervical os, without passage of products of conception and without evidence of a fetal or embryonic demise. The bleeding during a threatened abortion is typically mild to moderate, and the abdominal pain may present as intermittent cramps, suprapubic pain, pelvic pressure, or lower back pain.

It is important to note that not everyone who has bleeding in early pregnancy will miscarry, and most women with a threatened abortion go on to have a normal pregnancy. However, bleeding is the most predictive risk factor for pregnancy loss, and more than half of threatened abortions will abort. If a threatened abortion is suspected, patients should be evaluated by a healthcare professional to determine the best course of action. Treatment options may include watchful waiting, bed rest, medications, or other interventions depending on the individual case.