When Can Ultrasound Results Mean a Miscarriage?

An Ultrasound to Distinguish Miscarriage from Early Pregnancy

Ultrasound Scan
How can a miscarriage be diagnosed by ultrasound?. webphotographeer / Getty Images

If you're concerned that you may be miscarrying, you may wonder how a miscarriage is diagnosed. How can ultrasound help to determine if you are have an early pregnancy versus a missed miscarriage, and what are the limits of this test in early pregnancy?

Early Ultrasound - Early Pregnancy vs Miscarriage

When administering an early ultrasound exam, such as during the first trimester of a woman's pregnancy, it can be hard for medical professionals to distinguish an early pregnancy from a missed miscarriage.

A missed miscarriage is a pregnancy loss in which the embryo has either stopped developing or was never formed, but the mother is not yet having clear miscarriage symptoms such as vaginal bleeding or spotting, the passing of tissue through the vagina, and/or pain or cramping in the abdomen, lower back, or pelvic area.

Guidelines for Diagnosing Miscarriage Through Ultrasound

To avoid a misdiagnosis, doctors use specific guidelines to determine when ultrasound results may signal a miscarriage. For example, in a report by the Society for Obstetrics and Gynecology of Canada, researchers recommended that miscarriage be diagnosed if a transvaginal ultrasound reveals the following:

  • No heartbeat in an embryo larger than 5 mm
  • Gestational sac is larger than 8mm and has no yolk sac
  • Gestational sac is larger than 16mm and has no embryo

If this sounds confusing, you can learn more about how to understand early pregnancy ultrasound results.

In addition, if an earlier ultrasound revealed a fetal heartbeat and a subsequent ultrasound finds no heartbeat, this also indicates a miscarriage. Falling levels of hCG (human chorionic gonadotropin, a hormone that's made during pregnancy) alongside an ultrasound that shows an empty gestational sac or no fetal heartbeat may also lead to a miscarriage diagnosis.

How These Guidelines Vary

It's critical to note that different countries and different medical associations may vary in their exact approaches to the issue of distinguishing an early pregnancy from a missed miscarriage. And, of course, as scientific research on the topic evolves, guidelines may change.

The reason that guidelines such as these are important is because most pregnancy losses occur in the first trimester. In addition, there are several situations which can make it more difficult to make the distinction, in other words, there are several situations which can increase the risk of a misdiagnosis. These can range from an inaccurate estimation of your due date, to a vanishing twin, a condition in which one twin is miscarried while the other remains alive.

What if Your Ultrasound is Uncertain?

In following the ultrasound guidelines for diagnosing a miscarriage, there will be many times when the ultrasound cannot conclusively say if you have an early pregnancy or a missed miscarriage. In order to avoid the possibility of a misdiagnosis, your doctor may recommend waiting and repeating an ultrasound in a week. In a normal pregnancy, the gestational sac (and embryo if seen) should be significantly larger in one week, whereas a missed miscarriage will show no growth or only minimal growth.

During this week, if you have a missed miscarriage instead of an early pregnancy, you may develop symptoms of a miscarriage. It may be helpful to familiarize yourself with the most common signs and symptoms of an early miscarriage.

Calculating Miscarriage Risk

Calculating a mother's risk of pregnancy loss depends largely on her age. According to the American Congress of Obstetricians and Gynecologists, the risk of miscarriage for women changes significantly with age:

The Woman's AgeAverage Risk of Miscarriage
20-30 years old9-percent to 17-percent
35 years old20-percent
40 years old40-percent
45 years old80-percent

If You Experience a Miscarriage - Support and Coping

If you do experience a missed miscarriage, which can be extremely traumatic (both physically and emotionally), there are resources available that can help you and your partner get through this difficult period. Ask your doctor if there are any in-person support groups in your area, and/or seek out anonymous online support in one of the many online miscarriage support groups or support communities. You can also check out online resources like Miscarriage Matters, a site run by a charitable organization that offers online live chats. 

More Miscarriage Resources

If you're just hearing about missed miscarriages and more, you may be feeling confused about all of the terminology used to describe miscarriages, for example, terms such as a blighted ovum, a chemical pregnancy, a molar pregnancy, and more. Ask questions. If you don't understand something your obstetrician is saying, ask her to explain it in a different way. Wondering about the possibility of miscarriage, or coping with a miscarriage, is difficult enough when you are able to understand the medical lingo. It can be even more frightening if you feel like you are listening to a foreign language. Here are some answers to the questions people often ask with first trimester miscarriages, but write down any questions you have so that you remember to ask. Answers won't bring back a baby lost to miscarriage, but may help you as you cope in the weeks and months to follow.

Sources:

Ashoush, S., Abuelghar, W., Tamara, T., and D. Ajiobboury. Relation Between Types of Yolk Sac Abnormalities and Early Embryonic Morphology in First-Trimester Missed Miscarriage. Journal of Obstetric and Gynaecology Research. 2016. 42(1):21-8.

Morin, L., Cargill, Y., and P. Glanc. Ultrasound Evaluation of First Trimester Complications of Pregnancy. Journal of Obstetrics and Gynaecology Canada. 2016. 38(10):982-988.

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