1. Parenting
Pamela Prindle Fierro

Reader Question: Is It Possible to Only See One Baby on Ultrasound?

By September 16, 2010

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Q. Heather asks, "Is it possible to be pregnant with twins and it show up as a single pregnancy on the ultrasound?"

A. It is possible early in pregnancy, although it's fairly uncommon. However, it definitely can happen -- it happened to me!

2 week old twins

2008 Pamela Prindle Fierro, licensed to About.com, Inc.

I had an early pregnancy transvaginal ultrasound at seven weeks. Here is an actual photograph from that ultrasound. One healthy embryo was clearly identified and I went on my merry way through pregnancy. Then, several months later I went in for a routine twenty week ultrasound scan. Surprise! "You've got two!" (I'll never forget that moment of utter astonishment.)

What happened in this case was that my monozygotic twins were monochorionic, sharing a placenta and encased in a single chorion, the outer membrane of the sac. Basically they were so close together that one is shadowed behind the other. When viewed in a two dimenstional picture, all that is visible is the "top" twin.

So it is possible, just not very likely. Keep in mind that this picture is nearly fourteen years old; ultrasound technology has improved since then, and the rise in multiple births ensures that doctors and technicians are more adept at identifying multiples. Also, this was an ultrasound scan very early in pregnancy; I was only seven weeks along when this was taken. By twenty weeks it was exceedingly and unmistakably evident that there were twins, so a later ultrasound would be more reliable. There were also some other circumstances that kept the presence of twins from being revealed, including a lack of extreme symptoms such as nausea or fatigue and a rotating set of doctors so that no one person listened to the fetal heartbeat(s) more than once. I never measured large for gestational age, and I never had any of the common screenings that might raise a flag for multiples such as hCG or AFP.

Think You Might Be Having Twins?

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August 6, 2008 at 10:34 am
(1) Linda says:

I just had this happen to me. I had an early ultrasound (transvaginal) at 6w1d which showed 1 baby. 2 days ago (10w6d) I went for an ultrasound as part of the NT Scan and she said “Your having twins”. Obviously the first ultrasound missed one of the babies. I think if the ultrasound is very early they can miss one of the babies because they are so small at that point.

August 7, 2008 at 9:47 am
(2) julie says:

This happened to me, too, 4 years ago. I had a “regular” (not transvaginal) at 8 weeks, then was surprised at 20!

August 7, 2008 at 2:04 pm
(3) Leah says:

This happened to me. I am a twin and I had 2 ultrasounds, one at 9 wks and one at 16 wks and they didnt even look for twins. It was during my 22 wk ultrasound to find out the sex that we were shocked. There was definately 2 babies. I knew there was something different about this pregnancy considering I was in maternity clothes at 2 months.

August 12, 2008 at 8:33 am
(4) Karen says:

I didn’t find out I was having twins until I was 27 weeks!!! I didn’t have a first trimester ultra sound. I did have one at 19 weeks, but apparently a baby was hiding. At 27 weeks I had another ultrasound to figure out why I was so big….SURPRISE…you’re having twins!!!

August 12, 2008 at 10:54 am
(5) Greta Blancarte says:

Me too! One of my little rascals was hiding during our 9 week ultrasound and gave us a big surprise at 21 weeks.

August 12, 2008 at 6:00 pm
(6) Jennifer says:

This happened to me as well. The doctor suspected two embryos when he did a transvaginal ultrasound at 7 weeks. He had us wait a week and a tech repeated the ultrasound and was convinced that she only saw one. We were so relieved because we already have a 2 year old. We discovered there were two at the 20 week ultrasound.

September 21, 2010 at 8:15 am
(7) Juliet says:

It happened to me as well in 2008. We sow 1 baby at 3 weeks. At 6 weeks we were shocked to see two babies in one sac. It was scary but the doctor explained that it’s rare and unsafe(risk of Twin To Twin Transfusion Syndrome). the boys are 16 months old and healthy, very identical.

September 21, 2010 at 8:49 am
(8) faye says:

This also happened to me had a scan at 10 weeks then had the blood test at 16 weeks to be told i had a high level in my blood and to come in straight away for a emergency scan and to my joy/horror there were my two boys !!

September 21, 2010 at 11:04 am
(9) Claudia says:

Same thing here. Had a vaginal ultrasound at 8 wks – only one embryo. At 12 wks, we got our surprise – both are doing great! What? We had it set in our minds that we were having just one more. Only one placenta showed but they were separated by a hair-thin membrane. So, needless to say, I had a lot of dr appt’s! The twins were born at nearly 39 wks, 7lbs 6 oz and 7lbs! Oh, I had the doc check @ 8 wks for two as my mom’s a twin and her twin sister’s daughter had twins!

November 23, 2011 at 4:52 pm
(10) Derica says:

I am 19 weeks pregnant I had an ultrasound and there were 2 sacs but only one baby. What is that? Is that common? I live in the Bahamas and a little skeptical about the doctor.

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