During pregnancy, ultrasound can give doctors a good idea of how the baby is developing, and usually the news is reassuring. But sometimes ultrasound results can be confusing or concerning. Here are some of the most common concerns people have when ultrasound doesn't show the expected results.
Because the gestational sac appears fairly early on an ultrasound, seeing no gestational sac isn't a good sign. Sometimes the explanation is that the pregnancy is still too early, but other times, seeing no gestational sac may mean miscarriage or ectopic pregnancy.
When the gestational sac is smaller than expected, the reason may be that the pregnancy is not as far along as originally estimated, but the results could also be a sign of miscarriage. Usually doctors need a follow-up ultrasound to tell for sure.
The yolk sac should appear somewhere around the fifth or sixth week of pregnancy.
As with the above findings, a finding of no fetal pole could mean that the pregnancy was still too early to see the fetal pole -- or it could mean miscarriage.
Because the heartbeat appears only after the sixth or seventh week of pregnancy, a very early ultrasound can show no fetal heartbeat even in a viable pregnancy. But if the baby or sac measures beyond a certain length, seeing no fetal heartbeat can be conclusive for miscarriage.
A slower than expected fetal heart rate isn't a great sign in general and does mean higher risk of miscarriage. In some cases, however, it can normalize and the pregnancy may continue without further concerns.
The accuracy of ultrasound results depends on what is being measured and at what point during pregnancy, as well as the type of machine is being used and the skill level of the practitioner.