How soon can it be determined if a pregnancy is twins?

The title pretty much says it all…

If a woman is 6 or 7 weeks pregnant and one of those internal ultrasounds are done (you know, the ultrasound wand that they stick into your vagina), can the doctor determine if there are two embryos?

I know that an internal ultrasound at about 6 or 7 weeks can determine the size and age of an embryo (fetus?) so I would think they could tell if there were more than one embryo, right?


As my wife recalls, positive pregnancy test at two weeks, then we saw two sacs at four weeks and then the actual critters at six weeks.

Would there be a difference between identical and fraternal? I’d guess that fraternal would be more widely spaced and easier to differentiate.

I don’t know the answer, but ours were fraternal.

Around six weeks or so, they can identify the heartbeat on ultrasound, and yes, they will probably notice if there are two heartbeats thumpin’ away in there. (I have heard of cases in which the twins were positioned in such a way that it appeared there was only one heartbeat, but I believe these cases are rare.)

Mrs. Duaility, who is an LPN at a OB/GYN clinic, says a Quantitative (hormone) Test will tell the tale as soon as pregnancy is confirmed.

In my sons case it was at 12 weeks when it was discovered. Definitely 2 of them in there. Panic and hysteria ensued. Nothing improves an unexpected pregnancy more than twins :smiley:

A blood test can confirm quite early. Beta HCG levels should double approximately every 2 days during the first four weeks of pregnancy. Levels that are doubling faster than that or are significantly higher than would be expected for the gestational stage can be an indication of twins.

Hopefully a medical-type will be along shortly to tidy up my explanation and confirm accuracy.

Thanks everyone, that’s very helpful information!

OK- IAAD, and I started an O&G job two weeks ago, so I can give you some information, but this should in no way be taken as medical advice etc. etc.

short answer:
Yes, a scan at 6-7 weeks should tell us if we’re looking at a twin pregnancy. If they didn’t see a second baby, there isn’t a second baby to see.

Long answer:
Relying on HCG alone is not a good idea.
It’s not reliable as a one off measurment, and waiting 48 hours to get 2 in a row is much less convenient and reliable than doing a Transvaginal ultrasound scan (TVUSS).

TVUSS shows things on average 7-14 days earler than an abdominal USS, and although the probe looks remarkably like a curling iron, only the first 2-3cm actually goes in, so it isn’t as horrible as it first appears.

You should see gestational sacs from about 4 weeks.
If the sac is over 20mm your operator should see a foetal pole.
If the foetal pole is over 6mm, your operator should see a foetal heart.
If the sacs or foetus(es) are smaller, we are not able to confirm a viable pregnancy- usually we advise women to return for a further scan in a week to 10 days.

2 sacs, 2 babies, 2 heartbeats= twins (possibly identical, possibly fraternal)
1 large sac, 2 babies, 2 heartbeats= identical twins
2 sacs >20mm, 1 baby, 1 heartbeat= one pregnancy and either a clot above the sac giving the appearance of a second sac, or an early miscarriage of a second twin.

A significant proportion of people found to be pregnant with twins before 8 weeks will go on to have only a singleton pregnancy. In other words, the earlier you see twins, the more likely it is that the person will not go on to have twins.

The hospital where I work has a daily walk-in Early Pregnancy Assessment Clinic, for anyone in the first 12 weeks with any concerns (cramping, bleeding, hyperemesis, reassurance after previous early miscarriage etc). We give everyone who attends a TVUSS, and advise women who are found to have two gestational sacs before 8 weeks that there is a chance that one of the pregnancies won’t continue. If we’ve seen 2 healthy heartbeats, the chances smaller that we will lose one of the twins.

Thank you Irishgirl, you are awesome!

So the heartbeats can actually be seen in the TVUSS? Even at 5 or 6 weeks?

Also, I know it’s complicated, but what kinds of things cause a the loss of a twin embryo after it’s been determined early on? Does the woman usually have some sort of bleeding discharge when she loses one of the twin sacs? Or does it just get reabsorbed?

Also, while I’m at it, can I ask one more question? Let’s say a woman finds out she is pregnant around 5 weeks. Before that, she didn’t know she was pregnant. During the first 5 weeks she took the following medications: Benadryl, cough medicine, cold medicine (pseudoephedrine), birth control pills, Zoloft 100 mg, and drank heavily on one or two occasions (and also lots of caffeine).

Would there be any cause to believe that the fetus would be damaged from ingesting those things?

I don’t think that heavy drinking is as huge of a problem in the first few weeks. The eggs are not connected to the mother at this stage IIRC. When Iris was pregnant my mother had just died and we all drank a bit a couple of times. There were no problems with either the baby or the pregnancy.