The Yolk Sac–What to Expect on Ultrasound

What is the Yolk Sac?

the yolk sac

In this post, I’ll explain the yolk sac, its role in your pregnancy, what you should expect to see, and when we can expect to see it. Additionally, I’ll share an email I received from an anxious mama regarding an image her doctor gave to her. She didn’t see a yolk sac and was concerned one may not be there.

anxious mama: I recently received an ultrasound at 7 Weeks 5 Days. My doctor said everything looked great, and we were able to see its little heartbeat. When I got home and looked at the photo a little closer, I couldn’t find a yolk sac. Would you mind looking at it and letting me know if you can see a yolk sac or anything else you may notice? Thank you so much. This is my first pregnancy after having a miscarriage and I am slightly protective. 🙂

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In short, if there’s an embryo, a yolk sac must exist! I didn’t see a yolk sac in her image, either. That said, it may be positioned on either side of the embryo, in which case you may not be able to see it in your particular image.

What’s the Role of the Yolk Sac?

The job of the yolk sac provides nutrients for the embryo until the placenta develops. No yolk sac, no baby. Your baby cannot develop without it! When this happens, we’ll often see only a gestational sac with no yolk sac or embryo. This is called a blighted ovum. Of course, this is not a good pregnancy and must end. Though many women have said they felt so much better knowing this–it can be much more difficult to accept knowing a heartbeat started, then stopped.

So, if your doctor said all looks good and you see a heartbeat, there has to be a yolk sac in there somewhere.

When Can We See a Yolk Sac?

The yolk sac is typically seen somewhere after 5 Weeks gestational age, before we ever see an embryo at Week 6. We normally continue to see the yolk sac every week until somewhere around Week 12 or so, maintaining its same appearance. As we near the end of the 1st Trimester, however, we are less concerned about identifying the yolk sac. As long as Baby is growing appropriately, documenting it is not as important as it is in early pregnancy.

What Will You Expect to See on Ultrasound?

A yolk sac looks like a tiny white circle. Most often, you will see your embryo cuddling up against it. Below is an image of an embryo at 9 Weeks and a great image of the yolk sac right up against Baby’s bottom.

 

9 Weeks, 9 Weeks pregnant, pregnancy Week 9, yolk sac

Embryo – 9 Weeks

However, sometimes we are not able to obtain the yolk sac in the same image with the best view of your embryo or fetus. Check out the image of the twins’ yolk sacs below.

Yolk Sac, twins, twin yolk sacs

Twins’ Yolk Sacs – Week 6

Here you can see an image below of the same scan with just the embryos shown.

6w6d Dichorionic/Diamniotic Twins, 6 Weeks pregnant, 6 Weeks, 6 Week Twins

Twins – Week 6

I will also add here that I understand how frightening and what an anxious time it is for women to try again for Baby after a pregnancy loss. No matter how early someone miscarries, it’s still a loss and emotionally draining.

When a miscarriage happens very early in one’s pregnancy, we call it nature’s way of taking care of something which was not developing properly. From a human, spiritual, or emotional viewpoint, I like to think that Baby decided he or she needed a little more time! I always say our babies come to us when they are ready, not always when we are ready for them. They have to be ready for this great big world, too!

As providers, we don’t take special pains to give you an image of the yolk sac. It’s just not as doggone cute as your Little Sprout! 🙂

You can email me with your questions or Subscribe to send me your images for review!

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Thanks for reading!

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