Blighted Ovum: What the Scan Shows
A blighted ovum (also called an anembryonic pregnancy) is when a gestational sac develops in your uterus but no embryo forms inside it. It is one of the most common causes of early pregnancy loss, and receiving this diagnosis can be incredibly distressing. Understanding what the scan shows — and why doctors sometimes need more than one scan to be certain — can help you make sense of what is happening.
What Is a Blighted Ovum?
After a fertilised egg implants in the uterus, it normally grows into both an embryo and a placenta. With a blighted ovum, the placental tissue (trophoblast) begins to develop and produces hCG — which is why a pregnancy test will show positive — but the embryo itself does not form or stops developing at a very early stage, before it is visible on ultrasound.
Because your body is still producing pregnancy hormones, you may have experienced all the usual early pregnancy symptoms: nausea, sore breasts, missed period. This can make the diagnosis feel especially shocking.
A blighted ovum always results in miscarriage, either naturally or with medical assistance. It is not something that can be treated or reversed, and it is not caused by anything you did or did not do.
How It's Diagnosed
A blighted ovum is diagnosed through ultrasound — usually a transvaginal (internal) scan in early pregnancy, which gives a clearer picture than an abdominal scan at this stage.
A blighted ovum is diagnosed when:
- The gestational sac is large enough that an embryo should be visible
- No fetal pole or yolk sac is seen inside the sac
- Follow-up scans confirm no development has taken place
The size of the gestational sac matters greatly. When the sac measures around 20–25 mm or more (mean sac diameter) and there is still no visible embryo or yolk sac, the diagnosis of anembryonic pregnancy can be made with confidence. However, guidelines from the Royal College of Obstetricians and Gynaecologists (RCOG) and NHS early pregnancy units are cautious: a single scan is not always enough.
If your sac is smaller than the threshold for a definitive diagnosis, a repeat scan — usually 7–14 days later — will be arranged. This is to make absolutely sure the diagnosis is correct before any management decisions are made. Waiting for a second scan when you are already worried and upset is very hard, but it is the right approach.
What You Might See on the Scan
During the scan, the sonographer will look for:
- The gestational sac — a dark, fluid-filled oval shape in the uterus. This is usually visible from around 5 weeks on transvaginal scan.
- The yolk sac — a small bright ring inside the gestational sac, normally visible by 5–6 weeks. Its absence when the sac is large enough to show it is significant.
- The fetal pole — a small curved structure representing the developing embryo, normally visible by 6–7 weeks on transvaginal scan.
With a blighted ovum, the gestational sac will be present but appear empty — no yolk sac or fetal pole can be seen, even when the sac has grown to a size where they would normally be expected.
What Happens Next
Once a blighted ovum is confirmed, your early pregnancy unit (EPU) will discuss your options with you. There are three main approaches:
- Expectant management — waiting for the miscarriage to happen naturally, which can take a number of weeks
- Medical management — medication (usually misoprostol) to help the process happen sooner
- Surgical management — a procedure (ERPC or manual vacuum aspiration) to remove the pregnancy tissue
There is no single right answer. Your healthcare team will support you in making the choice that feels right for you, taking your health and circumstances into account.
Frequently Asked Questions
How is a blighted ovum confirmed?
It is confirmed through repeat ultrasound scans. The gestational sac must be large enough — typically around 20–25 mm mean sac diameter — with no visible embryo or yolk sac. Because dating can sometimes be uncertain, UK guidelines recommend a follow-up scan before a final diagnosis is made, usually one to two weeks after the initial scan.
Can a blighted ovum be misdiagnosed?
Yes, particularly if your dates are less certain than you think, or if ovulation happened later than expected. This is why your early pregnancy unit will arrange a second scan rather than diagnosing on the basis of one scan alone. It is rare but important — no one should be told a pregnancy is non-viable if there is any uncertainty.
Will this happen again?
A single blighted ovum does not mean it will happen again. Most people who experience one go on to have successful pregnancies. If you have three or more consecutive early pregnancy losses, your GP can refer you for investigations through the NHS recurrent miscarriage pathway.
Further reading:
For personalised advice about your scan results or your options, speak to your midwife, GP, or early pregnancy unit team.
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