Miscarriage is the loss of a pregnancy before 24 weeks. Most miscarriages occur during the first 12 weeks of pregnancy.
Experiencing bleeding during early pregnancy or being told that your baby’s heartbeat cannot be seen on ultrasound can be extremely worrying. However, bleeding or the absence of a visible heartbeat does not always mean that a miscarriage has occurred.
During the earliest weeks of pregnancy, a difference of just a few days can significantly affect what is visible on an ultrasound scan.
It is therefore important that miscarriage is diagnosed carefully, using established ultrasound criteria and appropriate follow-up when the findings are uncertain.
Key points
- Ultrasound is the most important investigation used to diagnose early pregnancy loss.
- The significance depends particularly on the size of the embryo.
- Sometimes an ultrasound scan shows a gestational sac within the uterus, but the developing baby (embryo) cannot yet be seen.
- A repeat ultrasound is sometimes necessary because a single examination cannot always establish whether a pregnancy is developing normally.
What are the symptoms of an early miscarriage?
The most common symptom of miscarriage is vaginal bleeding.
Bleeding may begin as light spotting or become heavier, sometimes accompanied by abdominal cramps, blood clots or the passage of pregnancy tissue. However, many women experience bleeding during the first trimester and continue to have a normally developing pregnancy.
Some miscarriages occur without any noticeable symptoms. This is sometimes called a missed miscarriage, when the pregnancy has stopped developing but there has been little or no bleeding or pain. The diagnosis may only become apparent during an ultrasound examination.
Symptoms alone cannot reliably confirm whether a pregnancy is developing normally.
Read more: Bleeding in Early Pregnancy: What Does It Mean?
How is miscarriage diagnosed on ultrasound?
Ultrasound is the most important investigation used to diagnose early pregnancy loss.
The examination assesses whether the pregnancy is located within the uterus, whether an embryo can be seen, how the pregnancy is developing and whether the baby’s heart activity is visible. Two ultrasound measurements are particularly important.
- Crown–rump length (CRL)
- This is the measurement of the embryo from the top of its head to the bottom of its body. When an embryo is visible, the clinician measures its size and checks for heart activity.
- Mean gestational sac diameter (MSD)
- The gestational sac is the small fluid-filled structure surrounding the developing pregnancy. If a gestational sac is visible but an embryo cannot yet be identified, the clinician measures the sac in three directions to calculate its average size.
These measurements help determine whether the pregnancy may simply be too early to assess or whether the findings suggest miscarriage. A diagnosis of miscarriage should not be made using pregnancy dates alone.
What does it mean if the embryo has no heartbeat?
The significance depends particularly on the size of the embryo. According to NICE guidance, when a transvaginal ultrasound scan is performed:
Embryo less than 7 mm, no heartbeat visible: the pregnancy may still be too early for a definite diagnosis. Another ultrasound scan should be performed after at least seven days.
Embryo 7 mm or more, no heartbeat visible: the findings are strongly suggestive of miscarriage.
These precautions are important because an incorrect diagnosis could have serious consequences for a pregnancy that is still developing.
An early scan showing no heartbeat should therefore always be interpreted in the context of the embryo’s measurements and the quality of the ultrasound examination.
Read more: When Can You See a Baby’s Heartbeat on an Early Pregnancy Scan?
Read more: No Heartbeat on an Early Pregnancy Scan: Is It Too Early?
What if there is a gestational sac but no embryo?
Sometimes an ultrasound scan shows a gestational sac within the uterus, but the developing baby (embryo) cannot yet be seen. This may simply mean that the pregnancy is earlier than expected.
To help understand the findings, the clinician measures the gestational sac in three directions to calculate the mean gestational sac diameter (MSD).
Gestational sac less than 25 mm, no embryo visible: it may be too early to make a definite diagnosis. Another ultrasound scan is recommended after at least seven days.
Gestational sac 25 mm or more, no embryo visible: this is strongly suggestive of miscarriage. However, a second opinion and/or a repeat ultrasound scan after at least seven days is recommended before confirming the diagnosis.
A pregnancy in which the gestational sac develops without an identifiable embryo is sometimes called an anembryonic pregnancy.
Your clinician should explain the measurements, whether the findings are conclusive and whether another scan is needed.
Why might I need another ultrasound scan?
A repeat ultrasound is sometimes necessary because a single examination cannot always establish whether a pregnancy is developing normally.
Pregnancy dates are usually calculated from the first day of the last menstrual period. Most pregnancy apps use the same approach and commonly assume a 28-day menstrual cycle, with ovulation occurring around day 14. However, ovulation does not always occur on day 14. Even women with regular menstrual cycles may ovulate several days earlier or later than expected. Women with longer or irregular cycles may have even greater variation. As a result, the pregnancy may be younger than the dates suggest.
During the earliest weeks, a difference of just three or four days can significantly affect whether an embryo or heartbeat is visible. In addition, when an embryo measures only a few millimetres, small differences in ultrasound measurements can influence the interpretation.
Waiting for an appropriate interval before repeating the scan reduces the risk of making an incorrect diagnosis. The repeat examination may demonstrate further growth and visible heart activity, or confirm that the pregnancy has not developed as expected.
Waiting for a repeat scan does not have a detrimental effect on the outcome of the pregnancy.
Is a transvaginal ultrasound necessary?
During the earliest weeks of pregnancy, a transvaginal ultrasound often provides clearer images than an abdominal scan.
This is because the ultrasound probe is positioned closer to the uterus, allowing the clinician to see very small structures in greater detail. A transvaginal ultrasound is considered safe during pregnancy and does not increase the risk of miscarriage.
From approximately seven weeks onwards, an abdominal scan can often demonstrate the gestational sac, embryo and heart activity, although visibility depends on several factors. If an abdominal scan does not provide sufficiently clear views, a transvaginal examination may be offered.
Can blood tests help diagnose a miscarriage?
Two hormones are sometimes measured during early pregnancy: human chorionic gonadotrophin (β-hCG) and progesterone.
Pregnancy hormone (β-hCG)
β-hCG is produced by the developing pregnancy and is the hormone detected by pregnancy tests. During the earliest weeks of a normally developing pregnancy, β-hCG levels generally rise. However, the rate of increase varies considerably between women. A single blood test cannot reliably tell whether a pregnancy is developing normally.
Sometimes, two blood tests taken approximately 48 hours apart are recommended to assess how the hormone level is changing. This is particularly useful when ultrasound has not yet confirmed where the pregnancy is located and the ultrasound scan is carried out less than 5–6 weeks’ gestation.
A rising β-hCG level does not, by itself, confirm that the pregnancy is developing normally, and it cannot establish whether the pregnancy is inside or outside the uterus.
Progesterone
Progesterone is a hormone that helps maintain the lining of the uterus and supports early pregnancy. Progesterone levels are generally higher in normally developing pregnancies and may be lower when a pregnancy is failing.
However, there is considerable overlap between normal and abnormal pregnancies. A low progesterone level does not, by itself, confirm miscarriage, and a normal level cannot guarantee that the pregnancy is developing normally. Research suggests that a very low progesterone level may indicate that a pregnancy is unlikely to continue, but the result cannot reliably establish whether the pregnancy is inside or outside the uterus.
For this reason, we do not recommend using progesterone blood levels alongside serial β-hCG measurements to diagnose a viable intrauterine pregnancy or an ectopic pregnancy when the pregnancy’s location is unknown.
Read more: Understanding hCG Levels in Early Pregnancy
Is progesterone treatment helpful?
Measuring progesterone in the blood is different from prescribing progesterone as a treatment.
There is evidence that progesterone treatment can improve the chance of a live birth in some women who experience bleeding during early pregnancy and have previously had a miscarriage. The evidence suggests that vaginal micronised progesterone 400 mg twice daily for women with early pregnancy bleeding, at least one previous miscarriage and an intrauterine pregnancy confirmed on ultrasound reduces the risk of miscarriage.
Progesterone treatment is not routinely recommended for every woman with early pregnancy bleeding, and it cannot reverse a miscarriage once pregnancy loss has been confirmed. Ultrasound remains the most important investigation for diagnosing miscarriage, with blood tests providing additional information in selected circumstances.
What happens after a miscarriage is confirmed?
Once a miscarriage has been confirmed, your clinician should explain the findings clearly and discuss the available management options. Depending on the circumstances, these may include:
- Expectant management
- Allowing the pregnancy tissue to pass naturally, with appropriate monitoring and follow-up.
- Medical management
- Using medication to help the uterus expel the pregnancy tissue.
- Surgical management
- Removing the pregnancy tissue through a procedure, when clinically indicated or chosen after discussion.
The most appropriate option depends on your symptoms, ultrasound findings, medical circumstances and personal preferences. If you are clinically stable, there is often time to consider the available options and make an informed decision. Your clinician should also discuss follow-up, the possibility of further bleeding or pain, and when urgent medical attention may be necessary.
Does one miscarriage mean I will miscarry again?
For most women, a single early miscarriage is an isolated event.
The majority of women who experience one miscarriage subsequently have a successful pregnancy. Extensive investigations are not usually required after one uncomplicated early miscarriage.
However, your clinician may recommend further assessment depending on your age, medical history, the circumstances of the pregnancy loss or previous miscarriages. Women who experience recurrent pregnancy loss may benefit from specialist assessment to investigate possible underlying causes and discuss care in a future pregnancy.
For further information, read our guide: Miscarriage in Early Pregnancy: How Likely Is It and Why Does It Happen?
When should I seek urgent medical attention?
If you are pregnant and experience heavy vaginal bleeding, severe or worsening abdominal pain, significant one-sided pelvic pain, shoulder-tip pain, dizziness or fainting, you should seek urgent medical assessment.
These symptoms may indicate significant bleeding or an ectopic pregnancy.
If you experience collapse, severe pain or heavy bleeding with faintness, call 999 or attend an Emergency Department immediately.
For other concerns, contact your local NHS Early Pregnancy Assessment Service, GP or NHS 111.
A diagnosis of miscarriage should never be assumed without appropriate assessment, particularly when the location of the pregnancy has not been confirmed.
Understanding the diagnosis of early pregnancy loss
Miscarriage is common, but its diagnosis must be made with care.
An early ultrasound may show a small embryo without visible heart activity or a gestational sac without an identifiable embryo. These findings can be concerning, but they do not always establish that the pregnancy has ended.
The most important principle is that miscarriage should only be confirmed when the appropriate ultrasound criteria and diagnostic safeguards have been satisfied.
Where uncertainty remains, a carefully timed repeat scan and a clear follow-up plan help ensure that the diagnosis is accurate and appropriately explained.
Related pregnancy guides
Frequently asked questions
What are the symptoms of an early miscarriage?
The most common symptom of miscarriage is vaginal bleeding. Bleeding may begin as light spotting or become heavier, sometimes accompanied by abdominal cramps, blood clots or the passage of pregnancy tissue.
How is miscarriage diagnosed on ultrasound?
Ultrasound is the most important investigation used to diagnose early pregnancy loss.
What does it mean if the embryo has no heartbeat?
The significance depends particularly on the size of the embryo. These precautions are important because an incorrect diagnosis could have serious consequences for a pregnancy that is still developing.
What if there is a gestational sac but no embryo?
Sometimes an ultrasound scan shows a gestational sac within the uterus, but the developing baby (embryo) cannot yet be seen. This may simply mean that the pregnancy is earlier than expected.
Why might I need another ultrasound scan?
A repeat ultrasound is sometimes necessary because a single examination cannot always establish whether a pregnancy is developing normally.
Is a transvaginal ultrasound necessary?
During the earliest weeks of pregnancy, a transvaginal ultrasound often provides clearer images than an abdominal scan.
Early pregnancy care at The Pregnancy Clinic
At The Pregnancy Clinic, early pregnancy ultrasound examinations are provided as part of a consultant-led pregnancy and fetal medicine service.
We understand that uncertainty about pregnancy development can be particularly distressing. Our approach is to assess ultrasound findings carefully, explain the significance of the measurements and provide clear advice about any further assessment required.
Where miscarriage is suspected or confirmed, we aim to provide sensitive, evidence-based guidance and appropriate recommendations for ongoing care.
Book an early pregnancy consultation → Book an early pregnancy scan →The Pregnancy Clinic is not an emergency service. If you experience severe pain, heavy bleeding, fainting or other acute symptoms, please seek urgent NHS assessment.