A blighted ovum, also called an anembryonic pregnancy, is one of the most common causes of miscarriage in the first trimester. It accounts for roughly half of all first-trimester pregnancy losses. In a blighted ovum, a fertilized egg implants in the uterus and a gestational sac develops, but an embryo either never forms or stops developing very early on.
How Often It Happens
Since about 10 to 15 percent of known pregnancies end in miscarriage, and blighted ovum is responsible for approximately half of those early losses, it affects a significant number of pregnancies each year. Many cases also occur before a person even realizes they’re pregnant, meaning the true frequency is likely higher than clinical numbers suggest. The pregnancy may seem to progress normally at first, with a positive test and early symptoms like nausea and breast tenderness, because the placenta briefly continues to grow and produce hormones even without an embryo.
The risk increases with maternal age. Research published in the International Journal of Reproduction, Contraception, Obstetrics and Gynecology found that the prevalence of blighted ovum rises significantly as maternal age increases. This follows the broader pattern of early pregnancy loss, where chromosomal abnormalities in the egg become more common over time.
Why It Happens
Most blighted ovums result from chromosomal problems at the moment of fertilization. The fertilized egg divides abnormally, and the resulting cells don’t have the genetic instructions needed to form an embryo. This isn’t caused by anything the mother or father did. It’s a random error in cell division that the body recognizes and stops developing.
In a normal conception, the fertilized egg divides and forms an embryo within about 10 days. With a blighted ovum, that process stalls. The gestational sac and early placental tissue may continue to develop for a while, which is why pregnancy tests remain positive and early symptoms can feel identical to a viable pregnancy.
When It’s Typically Discovered
A blighted ovum is usually diagnosed between seven and nine weeks of pregnancy, during a first-trimester ultrasound. At that point, a viable pregnancy would show a visible embryo with a heartbeat inside the gestational sac. With a blighted ovum, the sac appears empty.
Doctors use specific measurements to confirm the diagnosis. If a transvaginal ultrasound shows a gestational sac with a mean diameter of 25 millimeters or more and no visible embryo, that’s considered diagnostic. For smaller sacs, providers will typically wait and repeat the ultrasound at least seven days later before confirming the loss. This waiting period matters because dating can be slightly off, and a very early but viable pregnancy can initially look similar to a blighted ovum on ultrasound.
Why Pregnancy Symptoms Still Occur
One of the most confusing aspects of a blighted ovum is that your body may still feel pregnant. That’s because the placental tissue produces hCG, the hormone that triggers a positive pregnancy test and drives early symptoms like fatigue and morning sickness. With a blighted ovum, hCG levels can continue to rise even though no embryo is developing.
However, these hormone levels often rise more slowly than in a viable pregnancy. A single hCG blood draw can’t confirm or rule out a blighted ovum on its own, but a pattern of sluggish rises over multiple draws can raise suspicion. Ultrasound remains the definitive way to diagnose it.
What Happens After Diagnosis
Once a blighted ovum is confirmed, the pregnancy will not become viable. Your body may eventually miscarry on its own, which can take days to weeks after the diagnosis. Some people prefer to wait for this to happen naturally, while others choose medication to speed the process or a brief procedure to remove the tissue. The choice between these options is largely personal, and outcomes are similar across all three approaches.
Physically, the experience is similar to a heavy period, with cramping and bleeding that typically lasts a few days to two weeks. Your hCG levels will gradually drop back to zero over the following weeks, and most people get their next period within four to six weeks.
Chances of It Happening Again
Having one blighted ovum does not significantly increase your risk of having another. Because the underlying cause is usually a random chromosomal error, most people go on to have a normal pregnancy afterward. A single blighted ovum is not a sign of a fertility problem or a recurring condition.
If you experience two or more consecutive pregnancy losses, including blighted ovums, your provider may recommend testing to look for underlying factors like chromosomal issues in either partner, uterine abnormalities, or hormonal imbalances. But for the majority of people, a blighted ovum is a one-time event followed by a healthy pregnancy.