A miscarriage is the spontaneous loss of a pregnancy before the 20th week of gestation. A specific type, known as a missed abortion or missed miscarriage, involves a silent loss. This occurs when fetal development has ceased, but the body has not yet recognized the event or begun expelling the pregnancy tissue. Because the loss is not accompanied by typical symptoms like bleeding and cramping, it often goes undetected until a routine medical examination.
Defining Missed Abortion: The Silent Loss
A missed abortion is a pregnancy failure where the embryo or fetus is no longer viable but remains within the uterus. The fetal pole has stopped developing, or in some cases, failed to develop entirely (anembryonic pregnancy). The placenta and gestational sac are not immediately expelled by the body.
The term “missed” refers to the absence of typical warning signs that signal a miscarriage is underway. Many individuals continue to experience early pregnancy symptoms like nausea or breast tenderness because the placental tissue may still be producing hormones, including human chorionic gonadotropin (hCG). This hormonal activity prevents the uterine lining from shedding, delaying the onset of bleeding and cramping. The lack of physical symptoms means the loss can remain unknown until confirmed by medical professionals.
Identifying the Underlying Causes
The primary reason for a missed abortion is the non-viability of the developing embryo, most often due to random chromosomal abnormalities. These errors occur spontaneously during the division of the egg or sperm cells or shortly after fertilization. In the majority of first-trimester losses, the fetus has an incorrect number of chromosomes, making normal development impossible.
These genetic errors are typically sporadic occurrences and are not caused by anything the patient did or did not do. While advanced maternal age can increase the likelihood of these chromosomal issues, lifestyle factors, minor stress, or routine activities rarely cause this specific type of pregnancy loss. Less frequent causes include severe hormonal imbalances or structural problems within the uterus that impede implantation or growth.
Clinical Diagnosis and Confirmation
A missed abortion is frequently discovered incidentally during a standard prenatal ultrasound appointment when the patient has no reason to suspect a problem. The diagnosis is confirmed when the ultrasound image shows a gestational sac containing an embryo that lacks cardiac activity. Providers use specific measurements to ensure accuracy.
Ultrasound Criteria
- A Crown-Rump Length (CRL) of 7 millimeters or more without a visible fetal heartbeat.
- A mean sac diameter (MSD) of 25 millimeters or greater that contains no visible embryo.
In very early stages where findings are inconclusive, a repeat transvaginal ultrasound may be scheduled after 7 to 14 days to confirm the lack of developmental progression. Blood tests measuring the pregnancy hormone, hCG, are also used, showing levels that have plateaued or are declining instead of the expected doubling rate every 48 to 72 hours.
Management and Treatment Pathways
Once a missed abortion is confirmed, patients choose from three standard approaches for managing the uterine contents in collaboration with their healthcare provider. The decision is highly personalized, taking into account medical history, gestational age, and individual comfort level.
Expectant Management
This option involves waiting for the body to naturally expel the pregnancy tissue. This approach avoids medication and surgery and can be successful in a large percentage of cases, though it may take several weeks to complete. Monitoring is required to ensure the tissue passes completely and to watch for signs of heavy bleeding or infection.
Medical Management
This uses medications, typically misoprostol, a prostaglandin analog that causes the cervix to soften and the uterus to contract. This process mimics a natural miscarriage but expedites tissue expulsion, often within 24 hours. Sometimes, mifepristone is given 24 to 48 hours before misoprostol to increase the overall effectiveness of the treatment.
Surgical Management
This involves a procedure like Dilation and Curettage (D&C) or Manual Vacuum Aspiration (MVA). These procedures involve the gentle removal of the uterine contents, offering the advantage of a defined and immediate resolution. Surgical management is often chosen when a patient prefers the fastest physical recovery, or when expectant or medical management has failed or is not medically appropriate.