An ultrasound scan is the primary tool medical professionals use to diagnose pregnancy loss and assess the viability of an early pregnancy. It provides a definitive visual confirmation of whether the pregnancy is developing as expected. The images reveal the internal structures of the gestational environment, allowing for precise measurements and observation of developmental milestones. Understanding what a miscarriage looks like involves recognizing the normal structures that should be present and identifying when their size, shape, or activity indicates a non-viable outcome.
Visual Structures Used for Assessment
The sonographer focuses on three main structures that must appear sequentially and grow appropriately within the uterus during the first trimester.
The earliest structure is the Gestational Sac (GS), which appears as a small, dark, rounded area with a bright white rim representing the early placenta. The GS confirms the pregnancy is located inside the uterus and is typically visible around four and a half to five weeks of gestation.
Shortly after, the Yolk Sac (YS) becomes visible inside the GS, often around five to five and a half weeks. The YS appears as a small, round, bright white ring and provides nutrients to the developing embryo. An abnormally shaped or overly large yolk sac (typically greater than six millimeters) may raise concerns about viability.
The Fetal Pole (FP), the earliest visible embryo, appears as a small, linear or oval structure adjacent to the yolk sac, usually around six weeks. Once the FP is visible, its length, measured from crown to rump (Crown-Rump Length or CRL), becomes the most accurate way to estimate gestational age. These measurements are continuously compared against established growth charts to monitor progression.
Definitive Ultrasound Findings of Pregnancy Loss
A diagnosis of pregnancy loss depends on specific size and activity measurements that indicate the absence of a viable embryo.
The primary criterion involves the lack of Fetal Cardiac Activity (a heartbeat) when the embryo has reached a certain size. If the Crown-Rump Length (CRL) measures seven millimeters or more, and no heartbeat is visible on a transvaginal ultrasound, the pregnancy is definitively non-viable. This threshold is used because nearly all healthy pregnancies this large exhibit a detectable heart rate.
The second criterion concerns the Gestational Sac size without a visible embryo, often referred to as a blighted ovum. If the Mean Sac Diameter (MSD) is twenty-five millimeters or more and the sac appears completely empty, without a Yolk Sac or a Fetal Pole, this is a definitive sign of pregnancy loss. This indicates that the sac continued to grow even though the embryo never developed or stopped growing very early.
If initial measurements fall just below these definitive thresholds, the viability is uncertain, and a diagnosis cannot be made immediately. For example, if the CRL is less than seven millimeters without a heartbeat, or the MSD is between sixteen and twenty-four millimeters without an embryo, a repeat scan is necessary. Medical guidelines require a follow-up scan, usually seven to fourteen days later, to confirm the diagnosis. A diagnosis is then made if the repeat scan still shows no cardiac activity or if the sac remains empty and has grown to meet the definitive size criteria.
How Different Miscarriage Types Appear
Once a pregnancy loss is diagnosed, the ultrasound can further classify the type of miscarriage based on the contents remaining within the uterus.
Missed Miscarriage
A Missed Miscarriage, also known as a silent miscarriage, is characterized by the presence of an embryo or an empty gestational sac that meets the definitive non-viability criteria. The tissue has not yet been expelled from the body, and the cervical os remains closed. The patient may not have experienced noticeable bleeding or cramping, which is why the loss is often discovered during a routine scan.
Incomplete Miscarriage
An Incomplete Miscarriage shows retained Products of Conception (POC) within the uterine cavity. This typically appears as an irregularly shaped, heterogeneous mass—a mixture of tissue and blood clots—inside the uterus. This visual finding correlates with clinical symptoms where the patient is actively bleeding and has passed some, but not all, of the pregnancy tissue.
Complete Miscarriage
A Complete Miscarriage is diagnosed when the ultrasound reveals an empty uterus with a thin endometrial lining, typically less than thirty millimeters. There is no evidence of retained tissue or gestational structures. This scan confirms that all the products of conception have been fully expelled from the body, and often no further intervention is required.
Inevitable Miscarriage
An inevitable miscarriage is diagnosed when the ultrasound shows a non-viable pregnancy alongside an open or dilated cervix. This indicates that the expulsion of the tissue is imminent.