An anembryonic pregnancy, sometimes called a blighted ovum, is a type of early miscarriage where a fertilized egg implants in the uterus and a gestational sac develops, but an embryo never forms inside it. The pregnancy test comes back positive, early symptoms like nausea and breast tenderness can appear on schedule, and an ultrasound even shows a sac growing in the uterus. But when that sac reaches a certain size, it becomes clear that no embryo is developing within it. It is one of the most common causes of miscarriage in the first trimester.
Why the Pregnancy Starts but the Embryo Doesn’t
After fertilization, the egg divides into two groups of cells. One group is meant to become the embryo, and the other becomes the placenta and surrounding structures. In an anembryonic pregnancy, the cells that would form the placenta and gestational sac continue developing normally for a time, but the embryo cells stop dividing very early on. The result is an empty sac that looks like a pregnancy on ultrasound but contains no embryo.
Chromosomal abnormalities are the most common reason this happens. Studies using genetic analysis of blighted ovum tissue found chromosomal errors in about 62.5% of cases, a higher rate than in other types of early miscarriage. These errors typically occur during fertilization itself, when the egg and sperm combine with the wrong number of chromosomes. This is a random event. It does not reflect a problem with either parent’s health or fertility, and in most cases there is nothing that could have prevented it.
Why You Still Feel Pregnant
This is one of the most confusing parts of an anembryonic pregnancy. Your body produces the pregnancy hormone hCG when the fertilized egg attaches to the uterine wall, and the developing placental tissue continues releasing it even without an embryo. That hormone is what triggers nausea, breast tenderness, fatigue, and a positive pregnancy test. You can feel thoroughly pregnant because, hormonally, your body believes it is.
As the pregnancy fails to progress and hormone levels eventually decline, these symptoms tend to fade. Some people notice the change before their first ultrasound. Others feel completely normal right up until the scan reveals the empty sac. There is no reliable way to distinguish an anembryonic pregnancy from a healthy one based on symptoms alone.
How It’s Diagnosed
An anembryonic pregnancy is almost always discovered during a first-trimester ultrasound. The key measurement is the mean sac diameter, which is the average size of the gestational sac. If the sac measures 25 mm or larger and no embryo is visible inside, the diagnosis is definitive. At that threshold, the specificity is 100%, meaning there is no chance of mistaking a viable pregnancy for a failed one.
When the sac is smaller than 25 mm, the situation is less clear. A very early pregnancy may simply not have a visible embryo yet. In these cases, a follow-up ultrasound is scheduled. If a first scan shows a sac with a yolk sac but no embryo, waiting at least 11 days before rescanning is the standard approach. If the first scan shows a sac with no yolk sac and no embryo, the wait is at least 14 days. These intervals protect against misdiagnosis by giving a potentially viable pregnancy enough time to show growth.
Older diagnostic guidelines used smaller sac measurements (16 mm or 20 mm), but these carried a risk of false positives. The 25 mm cutoff, now adopted by major medical organizations internationally, eliminates that risk.
Three Options for What Happens Next
Once the diagnosis is confirmed, there are three approaches to completing the miscarriage: waiting for it to happen naturally, using medication to help the process along, or having a brief surgical procedure. None of these options affects your ability to get pregnant in the future, so the choice comes down to your preference, your comfort level, and your circumstances.
Expectant Management
This means letting your body pass the pregnancy tissue on its own. For some people, this feels like the most natural option. The tradeoff is uncertainty about timing and a higher chance of needing intervention anyway. In large studies, about 28% of people who chose expectant management ultimately needed a surgical procedure because the tissue didn’t pass completely. Bleeding lasts longer with this approach, averaging 12 to 17 days compared to 8 to 13 days with surgery. The need for a blood transfusion is rare (about 1.4%) but higher than with surgical management, where transfusions are essentially unheard of.
Medication
Medication can speed up the process. For anembryonic pregnancies specifically, success rates with vaginal medication are very high, reaching 100% in some clinical studies. Most people experience cramping and heavy bleeding within hours of taking the medication, and the process is typically complete within a few days. A second dose may be needed if the first doesn’t fully work. This option lets you manage the process at home on your own timeline while avoiding surgery.
Surgical Procedure
A dilation and curettage (D&C) is a short outpatient procedure that removes the pregnancy tissue directly. It’s the fastest and most predictable option. Bleeding afterward is minimal, and only about 4 to 5% of people need any additional procedure. Infection rates are similar across all three approaches. Recovery time and the number of days before returning to usual activities are comparable whether you choose surgery or expectant management.
Fertility After an Anembryonic Pregnancy
The outlook for future pregnancies is reassuring. After a single miscarriage of any type, the risk of miscarrying again in a subsequent pregnancy is about 20%, which is only slightly above the baseline risk for any pregnancy. Most people who experience an anembryonic pregnancy go on to have healthy pregnancies afterward. Even among people who have had more than one miscarriage, the majority eventually carry a pregnancy to term.
Because anembryonic pregnancies are overwhelmingly caused by random chromosomal errors during fertilization, having one does not indicate an ongoing fertility problem. There is generally no need for genetic testing or specialized workups after a single occurrence. Most doctors recommend waiting until after one full menstrual cycle before trying to conceive again, primarily so that dating a new pregnancy is easier.