The results of an ultrasound scan are separated into several categories, such as a viable intrauterine pregnancy, a pregnancy of uncertain viability or a delayed miscarriage. There are other categories that won’t be discussed in this blog.
A scan result of uncertain viability means that the sonographer cannot diagnose either a miscarriage or a viable pregnancy. This will understandably create worries and concerns for a couple. All sonographers (whether they are nurses, midwives or doctors) have to abide by strict guidelines, which prevent a couple ever receiving the wrong diagnosis. These National guidelines protect all unborn babies, couples and sonographers.
Uncertain viability is when a gestation sac less than 25mm can be seen in the correct site in the uterus, but the baby isn’t visible. The gestation sac might contain a yolk sac, which is thought to provide some early nourishment for the embryo (baby). Viability is also uncertain if an embryo under 7mm size is seen within the gestation sac, but there isn’t a visible heartbeat.
Both of these situations mean that the pregnant woman is offered a follow-up ultrasound scan. This will be 7-10 days later if the initial scan was performed transvaginally. However, if the scan was completed abdominally, the 2nd scan would be in 2 weeks. This is because (in most cases) a transvaginal scan is much more accurate.
Viability can be uncertain due to a variety of reasons. It might be that the pregnancy is simply earlier than expected. It can take several days for the egg and sperm to meet, then implant in the uterus. A longer menstrual cycle or irregular periods will result in an earlier gestation. Also when scanning very early in pregnancy, there can be a week or more difference between period dates and what you actually see. For example, you can be 6 weeks since a period and see a gestation sac of 5 weeks size, and there would be no cause for concern. We find most couples wait to book a private scan until 7-8 weeks of pregnancy.
Another reason for seeing less on scan, might be that the pregnancy has stopped growing. The follow-up scan will see if there has been any development. However, if there has been no growth in the gestation sac or baby, it would be safe to diagnose a delayed miscarriage. All women should be offered a second sonographer to confirm these findings, and will be referred into the NHS for continued care.
Although scan findings of uncertain viability can be worrying, your sonographer will always explain everything to you and refer you for NHS care if there is a clinical concern.
Angela Nicholson