Can Ultrasound Predict Miscarriage?
Measurements from early pregnancy ultrasound can determine whether your pregnancy will definitely end in miscarriage or is only suspicious for miscarriage.
Blood tests and ultrasound to monitor a pregnancy
There are two types of tests that fertility experts use to monitor an early pregnancy.
- Blood test to look at your hCG levels
- Ultrasound to look at a developing pregnancy
hCG levels can help predict a pregnancy that is going to miscarry. But today i'm going to discuss using ultrasound to predict miscarriage.
What doctors look for on an early pregnancy ultrasound
There are four important structures that doctors look for on ultrasound during early pregnancy.
The first is called a gestational sac. It is a collection of fluid formed by the cells of the developing placenta. The gestational sac in a normal pregnancy should be visible when a woman's hCG level is 2,000 or more.
Measuring the diameter of the gestational sac roughly corresponds to how far along the pregnancy has developed. We call it an empty gestational sac if there are no other structures inside. In other words only fluid is seen.
The next structure that becomes visible is called the yolk sac. This appears as a white ring located inside the gestational sac. The diameter of the yolks act can also be measured. I'll tell you why a little later.
Early Fetus and heart rate
On ultrasound the developing fetus is small white and shaped like a beam. When we see the developing fetus we will measure how long it is. This is referred to as the crown rump length or CRL.
The last thing that becomes visible are the pulsations of a couple of tubes which will eventually become the heart. For simplicity we just call this the fetal heartbeat but these tubes don't actually form into a heart for several more weeks.
We can divide ultrasound findings in early pregnancy and to those that are suspicious that a miscarriage might occur and those findings that definitely mean that a pregnancy is no longer viable and will miscarry.
Ultrasound signs that a pregnancy will definitely miscarry
There are four times when we can say a pregnancy is definitely not viable.
- You have measured the gestational sac diameter. It is 25 millimeters or more but there is no fetus visible
- If two or more weeks have passed since you saw an empty gestational sac and you still do not see a fetus with a heartbeat.
- If you did see a sack with the yolk sac on an earlier ultrasound but still do not see a fetus with a heartbeat 11 or more days later
- You have measured the fetus crown rump length. It is seven millimeters or bigger and there is no fetal heartbeat.
In all four of these examples, there is no chance that you will go on to have a live born baby.
A non viable pregnancy or miscarriage may not have any symptoms
You might not experience symptoms of a miscarriage however. Sometimes a non-viable pregnancy can hang out in the uterus for days, weeks or months without you ever knowing that anything is wrong.
Ultrasound signs that are SUSPICIOUS for miscarriage
There are many many times when we doctors are suspicious that you might have a pregnancy that will miscarry. But in these cases there is still some chance that everything may still turn out okay.
Anytime you don't meet the criteria I discussed earlier there is still a chance. For example, if you don't see a fetus but the sac only measures 20 millimeters instead of 25 millimeters, you cannot say with certainty that the pregnancy is non-viable. The same applies if you don't see a heartbeat but the fetus is only measuring five millimeters.
There are two other examples that I want you to be aware of:
1. If the yolk sac seems too big compared to the size of the gestational sac.
We know that these women are more likely to have a miscarriage but sometimes they will go on to deliver.
2. The heart rate of the fetus is less than 100 beats per minute.
In a healthy pregnancy, the heartbeat is usually going to be faster than that a heartbeat less than 100 means that there is a higher risk for miscarriage. Your doctor will want to keep doing ultrasounds to finally determine if you miscarry or not.