When a person discovers they are pregnant, early ultrasound scans confirm the placement and viability of the pregnancy. If the initial scan does not show the expected structures, it can cause anxiety. The term “blighted ovum” describes an early pregnancy loss where a gestational sac develops inside the uterus, but no embryo forms within it. Medically, this condition is more accurately referred to as an anembryonic pregnancy, meaning a pregnancy without an embryo. This diagnosis is a type of miscarriage where the body begins the process of pregnancy, but the development of inner structures fails very early.
Understanding Anembryonic Pregnancy
An anembryonic pregnancy begins with successful fertilization and implantation into the uterine wall. Following implantation, the outer layer of cells (the trophoblast) forms the placenta and secretes human chorionic gonadotropin (hCG) hormone. This hormone causes a positive pregnancy test and initial physical symptoms like nausea and breast tenderness. The gestational sac, the fluid-filled structure that surrounds the developing embryo, also forms and continues to grow for a time.
The continued growth of the sac and production of hormones explains why a person feels pregnant and receives confirmation, even without an embryo developing. The failure occurs in the inner cell mass of the blastocyst, the group of cells destined to become the embryo. This cluster of cells either fails to form or stops developing very early, usually before five to six weeks of gestation. The body eventually recognizes the pregnancy is non-viable, leading to a miscarriage, often later than expected due to continued hormone production.
Key Structures on Ultrasound and the Yolk Sac Question
The yolk sac is often the first visible structure within the gestational sac. It is a small, round structure that provides nutrients to the developing embryo before the placenta is functional. It typically becomes visible on a transvaginal ultrasound when the mean gestational sac diameter (MSD) measures approximately eight millimeters.
In a definitively diagnosed anembryonic pregnancy, the yolk sac is usually not present at the time of official diagnosis. The key diagnostic criterion is a mean sac diameter of twenty-five millimeters or greater with no visible embryo inside. If the gestational sac reaches this size, the embryo and yolk sac should be clearly visible in a normal, viable pregnancy.
An earlier scan may show a yolk sac without an accompanying embryo, a situation known as a pregnancy of uncertain viability. In these cases, the diagnosis cannot be confirmed immediately. A follow-up scan, typically performed eleven days later, is required to confirm non-viability if no embryo has developed. While a true anembryonic pregnancy confirms the absence of a developing embryo, an initial yolk sac may be present before the definitive diagnosis is established.
Genetic Causes of Blighted Ova
The underlying cause of most anembryonic pregnancies is related to chromosomal abnormalities within the fertilized egg. These errors occur spontaneously during cell division, resulting in an incorrect number of chromosomes or a structural defect that makes the pregnancy non-viable. The body recognizes this genetic flaw and halts development early in the process. This outcome is a natural biological response to prevent the growth of an embryo with profound developmental defects.
This is typically a random, non-inherited event not caused by anything the mother or father did. The genetic error is a singular occurrence tied to that specific egg and sperm combination. For the vast majority of individuals, an anembryonic pregnancy does not indicate an ongoing fertility issue or a high risk of recurrence in future pregnancies.
Options for Medical Management
Once an anembryonic pregnancy is diagnosed, individuals have three primary options for managing the miscarriage process.
Expectant Management
This involves waiting for the body to naturally recognize the loss and expel the pregnancy tissue. This option avoids medication and surgery but can be emotionally difficult due to the uncertain timeline, which may take several weeks. Patients choosing this path require close monitoring to ensure the process completes without complication.
Medical Management
This uses medication, most commonly Misoprostol, to induce uterine contractions and expedite the miscarriage. This approach is often preferred by those who wish to avoid surgery but desire a more predictable timeframe than expectant management allows. The medication is highly effective but may involve side effects like heavy bleeding, cramping, and nausea.
Surgical Management
This involves a procedure called dilation and curettage (D&C) to remove the tissue from the uterus. This is the quickest and most definitive method, providing immediate resolution of the physical process. While it is a minor surgical procedure, it carries the standard, low risks associated with any operative intervention. The choice among these options depends on the individual’s emotional state, medical history, and preference for speed versus invasiveness.