Miscarriage is typically diagnosed through a combination of ultrasound imaging, blood tests measuring pregnancy hormones, and a pelvic exam. No single test gives the answer in every case. Depending on how far along the pregnancy is and what symptoms are present, your doctor may need more than one round of testing, sometimes spaced days apart, before reaching a definitive diagnosis.
Ultrasound: The Primary Diagnostic Tool
A transvaginal ultrasound is the most reliable way to confirm or rule out a miscarriage. During this exam, a small probe is inserted into the vagina to produce a close-up image of the uterus. It’s more accurate than an abdominal ultrasound in early pregnancy because the probe sits closer to the uterus and can pick up details sooner.
What the doctor looks for depends on the stage of pregnancy. In very early weeks, they’re checking whether a gestational sac is present, whether it contains a yolk sac or embryo, and whether a heartbeat is visible. A heartbeat can be detected as early as 6 weeks with a transvaginal ultrasound, compared to about 7 weeks with an abdominal one. Even at 8 to 9 weeks, transvaginal detection is significantly more reliable.
Specific measurements determine the diagnosis. A large multicentre study published in The BMJ established the thresholds now used in clinical practice:
- Empty gestational sac 25 mm or larger: If the sac measures at least 25 mm across and contains no visible embryo or yolk sac, that confirms pregnancy loss with 100% specificity.
- Embryo measuring 7 mm or more with no heartbeat: If an embryo is visible and measures at least 7 mm from head to rump but shows no cardiac activity, that also confirms loss.
These cutoffs are deliberately conservative to avoid any chance of misdiagnosis. If measurements fall below those thresholds, the pregnancy could still be earlier than expected, so doctors will typically schedule a follow-up scan.
When a Repeat Scan Is Needed
Many people walk out of a first ultrasound without a clear answer, and that waiting period can be agonizing. A repeat scan is standard when the initial findings are uncertain. The timing depends on what was seen the first time.
If the first scan showed a gestational sac of 12 mm or larger but no embryo, a follow-up at least 7 days later checks whether an embryo with a heartbeat has appeared. If it hasn’t, that confirms miscarriage. For smaller sacs (under 12 mm), the wait is longer: at least 14 days, and the sac should have roughly doubled in size if the pregnancy is progressing. If an embryo was visible but had no heartbeat, another scan at least 7 days later checks again for cardiac activity. If there’s still none, the diagnosis is confirmed.
This cautious, step-by-step approach exists because dating errors are common. A pregnancy that’s a week earlier than expected can look nonviable when it’s actually fine. The repeat scan protects against that possibility.
Blood Tests for hCG Levels
Human chorionic gonadotropin (hCG) is the hormone your body produces after a fertilized egg implants. In a healthy first-trimester pregnancy, hCG levels roughly double every 48 hours during the first 6 weeks after conception. After that, the doubling slows to about every 4.75 days, and levels eventually peak around 100,000 IU/L before declining and stabilizing.
Your doctor will often draw blood twice, 48 hours apart, to see whether hCG is rising at the expected rate. A rise of at least 53% over two days has been associated with normal pregnancies when the initial level is below 5,000 IU/L. A slower rise, a plateau, or a declining level suggests the pregnancy may not be viable, though it doesn’t pinpoint the cause on its own. Falling hCG can indicate either a miscarriage or an ectopic pregnancy, which is why blood tests are almost always paired with ultrasound.
A single hCG reading is rarely enough to make a diagnosis. The trend over time is what matters.
Progesterone Levels
Some doctors also check progesterone, a hormone that supports early pregnancy. In pregnancies that end in miscarriage, progesterone levels tend to be significantly lower, typically ranging between 6.8 and 12 ng/mL, compared to the higher levels seen in viable pregnancies at the same gestational age. A very low progesterone level early on can raise suspicion, but it’s used as a supporting clue rather than a standalone diagnostic tool.
The Pelvic Exam
A pelvic exam gives your doctor immediate physical information. The key thing they’re checking is whether the cervix is open or closed, which helps classify what type of miscarriage may be occurring:
- Threatened miscarriage: You’re bleeding, but the cervix is closed and an ultrasound still shows a viable pregnancy. Many threatened miscarriages resolve on their own, and the pregnancy continues.
- Inevitable miscarriage: The cervix is open, meaning the body has begun the process of passing the pregnancy, even if tissue hasn’t been expelled yet.
- Incomplete miscarriage: The cervix is open and some pregnancy tissue has passed, but some remains inside the uterus.
- Missed miscarriage: The embryo has stopped developing or has no heartbeat, but your body hasn’t yet recognized the loss. The cervix stays closed, there may be no bleeding, and the diagnosis comes from ultrasound alone. This is often the most surprising type because there are few or no outward symptoms.
Blood Type Testing
If you haven’t had your blood type checked during this pregnancy, it will likely be tested during or after a miscarriage. The reason is your Rh factor, a protein on the surface of red blood cells. If you’re Rh-negative and the pregnancy was Rh-positive, your body could develop antibodies that attack red blood cells in a future pregnancy. An injection of Rh immune globulin prevents your body from producing those antibodies. This shot is only helpful if you haven’t already started making antibodies, so timing matters.
Genetic Testing on Pregnancy Tissue
After a miscarriage, your doctor may recommend chromosomal analysis of the pregnancy tissue, particularly if you’ve had more than one loss. About half of all first-trimester miscarriages are caused by chromosomal abnormalities in the embryo, and genetic testing can confirm whether that was the case.
This testing is most commonly recommended for recurrent miscarriage, when the pregnancy showed abnormalities on ultrasound, or when the cause of loss is unclear. Knowing the genetic result can be both medically useful and emotionally clarifying. If the loss was caused by a random chromosomal error, it’s unlikely to repeat. If a structural chromosomal issue is found that one parent carries, that information shapes planning for future pregnancies.
What the Testing Timeline Looks Like
For many people, the hardest part of miscarriage testing is how long it takes. If you go in with bleeding or cramping, you might get an ultrasound and blood draw that same day. But if the results are inconclusive, you could be waiting 48 hours for a second hCG draw, then another 7 to 14 days for a follow-up ultrasound. During that time, you may be told the pregnancy is of “uncertain viability,” which is the medical way of saying they can’t tell yet.
This pace feels slow when you’re living through it, but the delays are protective. The diagnostic thresholds used today were specifically designed to prevent false diagnoses. Before these stricter criteria were adopted, there were rare cases of viable pregnancies being misdiagnosed as losses. The current approach prioritizes certainty, even at the cost of a longer wait.