Two heartbeats but one sac on u/s?

[phoenix78]

Hey mamas,

Has anyone ever had two visible heartbeats on u/s but only one sac? Had u/s today to date pregnancy (since I apparently conceived first time I ovulated after weaning my 16 mo old - no LMP to date)...Baby was seen and was dated at 6 weeks 1 day. U/s tech showed us heartbeat and we listened in. Then she made a face, told me to move this way and that way (I have a tilted uterus) and my husband flashed me two fingers. I asked what that meant and he said "two heartbeats." I looked at u/s tech, who said she wanted to finish scanning before saying anything. She spent another 30 minutes moving all around what my husband said appeared to be a second fluttering heartbeat. No sac could be seen though. So tech said one baby but "could possibly" be two with one sac hiding. So I guess I have to wait for the dr. to review and then my midwife to call me with the official results.

Anyone ever had this happen and it was twins? This is an unexpected third pregnancy so the thought of twins is REALLY freaking me out. I was just getting used to the idea of baby #3.

PS - when I had my hcg tested two weeks ago, first number was 680 (at about 4 weeks) and second number 36 hours later was in the high 1500s.

[babyjelly]

Sometimes identicals share a sac. If I remember right, it means the egg split late.
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[MaerynPearl]

Agreed, one way they knew my doctors girls were identical before birth was they shared a sac. Unfortunately, that also put her at higher risk than most twin pregnancies.

[Melly24]

Babies sharing a sac are called monoamniotic twins.

[RedOakMomma]

No, twins sharing BOTH sacks are called monoamniotic twins. THAT is dangerous, but also very very rare.

Deep breath here.

I was "diagnosed" with monoamniotic twins eight years ago. The OB who helped remove my IUD at 6 weeks said there were two heartbeats, but only one sack. Of course, I googled it and totally freaked out (the OBs warnings didn't help, either). The information on monoamniotic twins, while hopeful, can also be very scary.

Turns out a lot of early twin pregnancies are misdiagnosed as monoamniotic twins.

Several weeks later, still stressed and worried, I had a higher level ultrasound with a perninatologist. Right away she was able to spot a thin, thin silvery line...my babies shared the OUTER sac, but the INNER sacs were separate. It's very, very common with identical twins--60% of them have this arrangement, from what I remember. It does NOT carry any increased risks for the twins...nothing that can't be dealt with at least (they'll share a placenta, which can be something needing monitoring, but in general things are totally normal with this arrangement).

It doesn't surprise me that an ultrasound tech wouldn't be able to spot another sac, or that there would be some confusion about where the babies are and where the sacs are. Don't let it worry you. Monoamniotic twins are so, so, SO rare...it's much more likely that you're dealing with uncertainty because of 1) low ultrasound quality and 2) a tech rather than a highly trained specialist. It's hard to see that whisper-thin inner amniotic sac in early ultrasounds--you need great equipment and a very trained doctor.

Wishing all the best for you, and congratulations!

[RedOakMomma]

http://en.wikipedia.org/wiki/Monochorionic_twins

This article is about monochorionic twins (twins sharing the outer sac, but not the inner sac). According to this article, 75% of identical twins have this sac arrangment, with about 25% having two sets of completely separate sacs. See? Very common and nothing to worry about.

If you have a monochorionic arrangement of twins, you can tell for sure they're identical. If, like my cousin, you have babies that have two completely separate sac/placenta systems, you have to wait and see if they're identical or if they're fraternal.

If you're worried or want more info, don't forget to post in the multiples parenting forum. LOTS of experts on this stuff there.

[phoenix78]

Thanks RedOak Mama, you just calmed me down a bit after I googled monoamniotic twins and started freaking out. As I mentioned, this was an unplanned pregnancy. DH is currently finishing school and does not have a job on the horizon just yet. I have a special needs 5 year old (who was a preemie following 4 months of bedrest) and an active 16 month old, so having 1 unplanned more child let alone two let alone 2 with a rare disorder is just more than my brain can handle today. I also had secondary infertility prior ot this pregnancy so I am still reeling that I could even get pregnant without using meds like the last 2 times.

I'm really hoping that my midwife will have more info after the radiologist reviews the scan. I think I'll also ask for a follow-up hcg and also another scan a little further along with a pernatologist. Trying not to get too far ahead of myself.

[butterflies]

I had an early u/s at 6w5d and it was very tough for them to visualize that thin inner membrane. The tech called in the dr who is a perinatologist specializing in twin pregnancies and they both looked from multiple angles trying to get a good look. They eventually felt reasonably sure that they could see it-- they showed me just a tiny "blip" on the screen, only a couple pixels wide.

I absolutely wouldn't worry this early on-- mono/mono twins are really very rare. They will likely ask you to do a repeat scan in 2-3 weeks and if there's a membrane, it will become much clearer!

[phoenix78]

Only One - So They Say

Sorry for the delayed update. The radiologist's report said there was only one baby. The suspected "blip" the technician thought was a heartbeat was apparently free floating fluid from a ruptured cyst on my right ovary (so says the report the midwife received). Hoping they are right and I don't go back for my 20 week u/s and find out there are two in fact! One was enough of a surprise for now. Thanks for sharing your wisdom mamas.