How Is a Missed Miscarriage Diagnosed?
A missed miscarriage (also called a silent or missed abortion) is when a pregnancy has stopped developing but there are no obvious signs like bleeding or cramping — you may still feel pregnant. Because there's often nothing physically alerting you that something has changed, the diagnosis is usually made at a routine or reassurance scan, which can make it a particularly disorientating shock. Here's exactly how sonographers and doctors confirm it, and why they're careful to never rely on a single scan alone.
What happens during the scan
An ultrasound is the main way a missed miscarriage is identified. The sonographer will look for two key things:
- A fetal heartbeat, checked using the ultrasound screen once the pregnancy is far enough along for one to normally be visible
- The crown-rump length (CRL), a measurement of the baby from head to bottom which helps estimate how many weeks along the pregnancy is
If no heartbeat is seen and the CRL measures 7mm or more, this is generally considered reliable evidence that the pregnancy has stopped. However, if the measurement is smaller than this, or your dates are uncertain (for example with irregular cycles or an unclear last period date), the sonographer usually cannot give a definite diagnosis at that visit.
Why a follow-up scan matters
Doctors are deliberately cautious here because early pregnancy dating isn't always exact, and a heartbeat can sometimes be too early to detect rather than absent because of loss. Where the picture isn't completely clear, you'll usually be offered:
- A follow-up scan, typically 7 to 14 days later, to check for any change or growth
- Blood tests measuring hCG (human chorionic gonadotropin) levels, sometimes repeated 48 hours apart — a healthy early pregnancy usually shows rising hCG, while falling levels support a diagnosis of loss
- Clear written information and a contact number so you know what to do if you have questions or new symptoms before the follow-up
This two-step process exists to protect against a wrong diagnosis, not to withhold bad news unnecessarily. It's always reasonable to ask for a follow-up scan if you feel uncertain about a result.
Getting support after diagnosis
Once a missed miscarriage is confirmed, your midwife or doctor will talk you through your options for managing it — including waiting for it to pass naturally, medication, or a minor surgical procedure — and there is no rush to decide immediately unless there's a medical reason to. Ask for written information to take away, and don't hesitate to request a second scan opinion if anything about the diagnosis feels unclear.
Frequently Asked Questions
Can a missed miscarriage be misdiagnosed?
It's uncommon once the criteria are properly met, but the risk is highest when dates are uncertain or the crown-rump length is small. This is exactly why a follow-up scan one to two weeks later is standard practice before a final diagnosis — never feel you have to accept an uncertain result without one.
What happens after a missed miscarriage diagnosis?
Your healthcare team will discuss your options for managing the miscarriage: expectant management (waiting for it to happen naturally), medication to help your body pass the pregnancy, or a surgical procedure. You'll usually have time to consider what feels right for you, along with information and support contacts.
How long can a missed miscarriage go undetected?
This varies significantly between pregnancies, which is part of why it can feel so shocking — some women have no symptoms at all until a routine scan. If you're ever concerned about reduced symptoms or a "gut feeling" that something isn't right, contact your midwife or early pregnancy unit rather than waiting for your next scheduled scan.
This article is for informational purposes only and does not constitute medical advice.
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