The Vascular Shadow

That is what I am calling the mass/clot/twin in the gestational sac because that is what it looked like, a shadow of the embryo, a kind of pulsing mass.  The side view of the gestational sac and the embryo looked normal.  When viewed from an angle you could see what looked like a shadow.  The doppler view showed a shape that looked similar to what a fetal heart would look like in doppler, which is where the possibility of a twin came from, but (as CJ asked in the comments) there was not a second heart beat detected.  So I think chances are low that it is a twin.

I've done so many ridiculous google searches: large umbilical cord at 8 weeks, abnormal 8 week ultrasound, abnormal umbilical cord, blood clot in umbilical cord, blood clot in gestational sac, hidden monoamniotic twin, mass in gestational sac.  I don't recommend image searches for these keywords.

The only thing I can find that sounds at all similar to what I have is a 2009 thread from MedHelp.  Here are a few posts:

I'm 7 weeks, 3 days along and the baby looks fabulous, heart just beating away. BUT, a big fat BUT, there is some sort of mass inside the gestational sac that the dr is very concerned about. ...She said its not something they see often therefore she didn't want to tell me too much. She said it could be a cyst or a blood clot that could absorb into the placenta...

Someone responded with,

I have the exact same thing!! [The] ...sac has a mass exactly like you described, I am 7w0d. Baby's heart and growth are perfect, but I am also going to see a specialist to check out what this could be. My endocrinologist has never seen anything like this.

and someone else followed,

I am in the same boat as you two!! I had my first sono on Tuesday, I am 7 wks 5 days and my sono showed an abnormal mass in my gestational sac. Baby was there, normal growth size, and had a heartbeat. I went back on Thursday for another sono and my doctor was still unsure of what was going on.

yet another,

I have the same thing. I went in for an ultra sound at 7 weeks 5 days. And they found this mass of i dont know what, next to the baby but not attached to it, within the sac.

and this that was more helpful and detailed,

Several possibilities were discussed with me ranging on the less scary end from a blood clot, a cyst, a twin that would be resorbed; to a few scarier possibilities like a partial molar pregnancy to tropoblastic disease. ...I was sent two weeks later (to let everything grow a bit, but still a long wait) to a high risk specialist for an ultrasound, hoping that since they see more unusual cases and might know what it is.  The doc was still unsure of what it was, thought possibly a placental cyst or on the scarier end, an acardiac twin (which would draw blood and vital nutrients away from the growing embryo and not allow it to survive).  They were still unable to tell 100% if it was attached to the embryo but they didn't think it was.  

Two of the responders eventually returned to the thread to follow up on their situation.  They were both positive outcomes,


I dont remember what mine looked like. All I know is that it was as big as fingertip. As my pregnancy went on, it disappeared completely. My baby is now 3 mons old and she is perfectly fine. 


and

I am now the proud mama of 4 month old Nathan! My mass turned out to be a placental cyst which eventually disappeared....

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I'm still not freaking out about what I saw.  There is absolutely nothing I can do at this point but hope the embryo continues to grow and whatever it is will resolve itself soon.    Nothing is ever easy.