Miscarriage and Ultrasound — What a Scan Can and Cannot Detect

No. This is asked far more often than it is said out loud, so it deserves a direct answer rather than a hedge. Diagnostic ultrasound — including transvaginal scanning — is not known to cause miscarriage. It uses sound waves rather than radiation, it has been used in pregnancy for more than fifty years, and there is no evidence that scanning causes pregnancy loss.

The specific worry about internal (transvaginal) scans is worth addressing properly, because the anxiety is usually anatomical. The probe goes into the vagina only. It does not enter the cervix, it does not enter the womb, and it does not touch the pregnancy. It sits close enough to see clearly — which is the entire reason it is used this early — while remaining outside the uterus altogether. A scan that feels firm or uncomfortable is not damaging anything, and a “rough” scan cannot dislodge a pregnancy.

Light spotting after an internal scan happens occasionally and is not a sign of harm. The cervix carries a rich blood supply in pregnancy and becomes more delicate, so slight contact can produce a small amount of pink or brown discharge that settles within a day. Heavy bleeding is different and should be assessed — not because the scan caused it, but because bleeding in pregnancy always warrants review.

What is true is the sequence people notice: a scan happens, and a miscarriage follows. The scan did not cause it. Early pregnancy loss is overwhelmingly caused by chromosomal changes present from conception, and where a pregnancy was already going to end, no imaging changed that. Our guide to ultrasound safety covers the physics and the monitoring in full.

Missed (silent) miscarriage. The pregnancy has stopped developing but the body has not yet recognised it — no bleeding, no pain, sometimes pregnancy symptoms continuing. It is found on a scan that was expected to be routine, which is precisely why it lands so hard. The scan shows an embryo without cardiac activity, or a sac beyond the size threshold with nothing inside.

Anembryonic pregnancy (blighted ovum). A gestational sac develops but an embryo never does. Diagnosed when the sac reaches 25mm or more with no embryo visible, usually confirmed on a repeat scan.

Incomplete miscarriage. Bleeding has begun and some pregnancy tissue remains in the uterus — described on a report as retained products of conception. This finding guides whether treatment is needed or whether waiting is reasonable.

Complete miscarriage. The uterus is empty and the lining thin, indicating the process has finished. If nothing was ever seen on a previous scan, an empty uterus alone cannot confirm this — an ectopic pregnancy has to be excluded first, usually with hCG blood tests.

Threatened miscarriage. Bleeding in early pregnancy while the scan still shows a heartbeat and appropriate growth. It is a description of symptoms, not an outcome — many such pregnancies continue perfectly normally, which is worth knowing if this is the phrase you were given.

Generally, no. Once the uterus has healed and the lining has regenerated — usually within weeks — an ultrasound cannot tell that a miscarriage happened months or years earlier. The uterus does not keep a visible record of it. A scan performed shortly afterwards may show retained tissue or a thickened lining, but that window closes quickly.

Occasionally a scan shows a consequence rather than the event itself — scar tissue following a surgical procedure, for example — but a normal scan does not mean a past loss did not happen, and no one should feel their experience needs imaging to be believed. If you are being assessed after recurrent miscarriage, ultrasound has a genuine role in looking at the shape of the uterus and the ovaries as part of a wider set of investigations arranged through your GP or a specialist.