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Dr. C.
Dr. C., Board Certified
Category: OB GYN
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OB GYN

Can an early ultrasound give an accurate prediction of conception

date?
Submitted: 4 years ago.
Category: OB GYN
Ask Your Own OB GYN Question
replied 4 years ago.

Dr. Collins :

I can help you.

Dr. Collins :

An early ultrasound is the most accurate way to predict conception date.

Dr. Collins :

The only thing more accurate is if you have IVF or only one possible day.

Dr. Collins :

An ultrasound done between 6-10 weeks is especially accurate but anything below 12 weeks is very accurate.

Dr. Collins :

After that, the baby will grow at different rates based on genetics, nutrition, etc.

Dr. Collins :

But before 12 weeks, babies all grow at the same rate under normal circumstances.

Dr. Collins :

Any questions?

Dr. Collins :

If not please click accept.

Customer:

if you have sex with 2 partners 14 days apart...would it be possible to rule one out based on ultrasound dating?

Dr. Collins :

Absolutely.

Customer:

really?

Dr. Collins :

If you have an ultrasound before 12 weeks, we can nail it down.

Dr. Collins :

Oh yes.

Dr. Collins :

The viation of ultrasoun before 12 weeks is just a few days.

Dr. Collins :

variation

Dr. Collins :

It's much harder if there are only a few days between the possible dates of conception.

Dr. Collins :

14 days is plenty.

Dr. Collins :

And harder later in the pregnancy.

Customer:

ok so i had an ultrasound done on 2/24 that dated the pregancny at 5 weeks 5 days and another on 2/27 that dated the pregnancy at 5 weeks 2 days....that is a 6 day difference....that is pretty big right?

Dr. Collins :

Let me calculate it.

Dr. Collins :

So conception was somewhere aroun January 30th to February 5th range.

Dr. Collins :

That is a pretty tight range

Dr. Collins :

What were the 2 potential conception dates?

Customer:

well there is january 14th with one person and then january 27th and 29th with the other

Dr. Collins :

Ultrasounds are a little more accurate past 6 weeks because the fetus is easier to see.

Dr. Collins :

The 14th is out.

Customer:

january 14th used a condom one time to completion and then no condom second time but no ejaculation second time

Dr. Collins :

Conception was from the sex on the 27-29

Customer:

i also took the morning afterpill....does that affect ovulation?

Dr. Collins :

The 14th is not the father.

Dr. Collins :

If you got pregnant on the 14th, than the ultrasound would've show 8 weeks.

Dr. Collins :

They would not have made an error confusing a 5+ week with an 8 week pregnancy.

Dr. Collins :

The only way is if the pregnancy ended in miscarriage and the baby stopped growing.

Customer:

i google way to much...so here is my question...isn't it possible for sperm to live in vagina for 7 days and then take an addition 14 days to implant?

Dr. Collins :

Morning after pill can delay ovulation.

Customer:

so doesnt that make it possible to the the 14th?

Dr. Collins :

Yes sperm can live in the vagina for 7 days, and yes it can take up to 14 days for implantation but during those 14 days, the baby is already growing.

Dr. Collins :

If you go on to have a healthy pregnancy, than it cannot be from the 14th.

Dr. Collins :

If you go on to have a miscarriage, than it can be either.

Customer:

should i be worried about the difference in ultrasound dates?

Dr. Collins :

No, babies during the 5th week are hard to measure.

Dr. Collins :

They are much easier to measure between 6-12 week.

Dr. Collins :

If you can, get a repeat ultrasound in a couple of weeks.

Dr. Collins :

That will settle it.

Dr. Collins :

If the pregnancy is healthy, the growth will be good, the heartbeat will be clear and the measurement most accurate.

Dr. Collins :

I do not think you got pregnant from the 14th if you have currently a healthy pregnancy.

Dr. Collins :

Any other questions?

Customer:

are hcg levels a good indication of a healthy pregnancy

Dr. Collins :

If you watched them taking the measurement, you saw how small it is.

Dr. Collins :

It depends alot on where they put those little white cross markers.

Dr. Collins :

If they juggle their hand a little while tapping it into position, it can change the day byt a few days when they are so small.

Dr. Collins :

Yes, if you get 2 hcgs 48 hours apart, than it should almost double in value.

Dr. Collins :

If it doesn't clearly double, than getting a third one in another 48 hours will usually settle the question.

Dr. Collins :

Anything lese?

Dr. Collins :

If not please click accept so I get credit for my time and advice.

Customer:

so if this is a healthy pregnancy you believe there is no way it could be from the 14th?

Dr. Collins :

The bhcg should be steady going up just under double each time.

Dr. Collins :

yes that is correct.

Customer:

is cramping this early normal?

Dr. Collins :

Yes cramping is normal as the implantation takes hold.

Dr. Collins :

It is normal.

Dr. Collins :

Even a little spotting can be ok.

Customer:

is it too early to tell if this is a healthy pregnancy?

Dr. Collins :

No, this is a good time to ask for the hcgs

Dr. Collins :

Get 3 of them 48 hours apart and that will give you the answer.

Customer:

i had them done on 2/20 at 2846 and again 39 hours later on 2/22 and the were 4296....should i have gotten another one? and do hcg levels correlate to what can be seen on an ultrasound?

Dr. Collins :

Yes one more would be helpful.

Dr. Collins :

I need to do something for a few minutes, let me look at that number better in a few minjutes. It didn't quite double.

Dr. Collins :

Ok, now I can concentrate again.

Dr. Collins :

So the second one was drawn a bit early so the known calculations can't be run on the number.

Dr. Collins :

So yes getting a thrid one even at this stage would be helpful.

Dr. Collins :

No the numbers do not correlate with what is seen on the ultrasound.

Customer:

should i request it from my doctor?

Dr. Collins :

Yes you can.

Dr. Collins :

That will be the fastest way to determine if the pregnancy is healthy.

Dr. Collins :

Alternatively, repeating the ultrasound 1 week after the last one will also be able to tell.

Customer:

it appeared as though there may have been a yolk sac...is that a good sign?

Dr. Collins :

Yes, we like a normal yolk sac.

Dr. Collins :

That decreases the risk of miscarriage.

Dr. Collins :

Anything else?

Customer:

no...thank you! but knowing me i will ask all these questions to someone else again!

Dr. Collins :

Ok, that's fine, it's always get to get more opinions, but be sure to click accept so we get credit for our time and we don't mind:)

Customer reply replied 4 years ago.
Hi....I had an ultrasound done today and the average measument taken was 6 weeks 0 days. I belive the sac measured at 5 weeks 5 days and the fetal pole at 6 weeks 3 days...there was a heartbeat of 114....is this enough evidence that this is a normal healthy progessing pregnancy?
Dr. C., Board Certified replied 4 years ago.
Let me review the above info. So the ultrasound on 2-27 = 5w2d, today 3 days later, it is showing 6w 0d. SO far so good. But the ultrasounds are too close together to be certain. The fact that it did increase in size and that there is a heartbeat are both very good signs. I usually don't repeat the ultrasound any sooner than 1 week apart because especially at small sizes, it's hard to control the little white cross calipers. SO far things seem fine, looking good for guy 2 and a healthy pregnancy but one more check with ultrasound in 1-2 weeks will be much more to go on. Please click accept and follow-up questions are always welcome.

Customer reply replied 4 years ago.

ok thanks

Dr. C., Board Certified replied 4 years ago.
Once you have the next ultrasound, I can interpret that information for you on this same thread if you like. Just click accept now so that I can stay in the loop. Good luck!
Customer reply replied 4 years ago.
how confident medically speaking would you be that it truly is guy number 2?
Dr. C., Board Certified replied 4 years ago.
At this point I would say 98 %. With one more ultrasound showing good growth, I would move to 100%.
Customer reply replied 4 years ago.
thank you so much!
Customer reply replied 4 years ago.

Hi Dr. Collins,

How possible is it for me to go into an ultrasound next week and have it show me two weeks further along than previously thought?

Dr. C., Board Certified replied 4 years ago.
Close to zero chance. Ultrasounds this early in pregnancy do not vary by more than a few days. It's unheard of for there to be a difference of more than 7 days. Keep me posted. More questions?
Customer reply replied 4 years ago.

Google is my worst nightmare...and I had read that doctors have missed the "baby" when measuring not to mention an expert on here has told me that as well. I am sorry to ask so many questions...but this really does affect the rest of my life. Also, for about a week I was really not eating well...I would say less than 500 calories a day...i was still taking the prenatal vitamins though....could this have affected the growth of the baby on the utlrasound?

Dr. C., Board Certified replied 4 years ago.
It is rare but yes, the ultrasound techs or docs can miss a very early pregnancy. But you already have had 2 ultrasounds that matched and showed good growth in between. It is very unlikely that they would get it wrong by 2 weeks twice. No your diet at this stage of pregnancy did not influence the growth of the baby. This is the reason that ultrasounds at this stage are so accurate. All the babies grow at the same rate no matter what is going on with a few very specific exceptions. Your low caloric intake was not enough to affect the babies growth at this stage.
Customer reply replied 4 years ago.
Here is some more information I would like your opinion on...I did have a period that started somewhere between the 6-8 of January. I had sex on the 14th and took the morning after pill on the 16th. I then thought I had my period on jan 22-25th (normal for me is 5-7 days)...could this just have been withdrawal bleeding or is it likely that this was actually my period?....
Dr. C., Board Certified replied 4 years ago.
For 1-2 months after taking the morning after pill, your bleeding will be off and it will not be possible to be sure whether it was just withdrawal bleeding or a true period. Based on the starting day of your early January period, it is more laikely that all the bleeding you had in January after the Plan B was just withdrawal bleeding from the medication.
Customer reply replied 4 years ago.
so that would mean that there was no egg??
Dr. C., Board Certified replied 4 years ago.
It could be that there was no egg that month. The morning after pill most likely delayed the release of the egg to later in the month. Also if there was an egg and it was fertilized, than the medication prevented implantation.
Customer reply replied 4 years ago.
because if the egg would have implanted then...it would most definitely have showed on the ultrasound?
Dr. C., Board Certified replied 4 years ago.
Yes.
Customer reply replied 4 years ago.
so this again just leads us to guy #2
Dr. C., Board Certified replied 4 years ago.
Yes, we are already at 99+% and the next ultrasound will get it to 100%. Hang in there. Please click accept so I get credit for today. When you have the next report you can continue in this thread.
Customer reply replied 4 years ago.
is there a such thing as a non-invasive prenatal paternity test? Have you heard anything about this? It says it "isolates fetal DNA from the mother's blood". I almost feel like this might be a scam but I was just curious if you have ever heard anything about this
Dr. C., Board Certified replied 4 years ago.
Oh yes I did see this question yesterday. Yes they can isolate fetal cells from the mothers blood. Let me check on the reliability of this testing and get back to you. I will give you the best answer possible. Give me a few minutes. I need to attend to something else but should be back to you within 30 minutes.
Dr. C., Board Certified replied 4 years ago.
Yes, I have checked reliable research bases and see that this technology is well tested and accepted as accurate in the medical community. Testing requires your blood draw and the father you want to either exclude or include. Testing requires that you be further along in the pregnancy however. The earliest that I saw this was possible was 10-11 weeks but some places require even further along, around 14 weeks. The further along you are in the pregnancy, the more likely that there will be babies DNA in your blood. Please click accept so I get credit for checking into this and above conversation. Happy to answer any more follow-up questions you have for the rest of the day as my time permits. Thanks
Customer reply replied 4 years ago.
Could you please refer me to your reliable research? I am just nervous about paying a ton of money for a scam?
Customer reply replied 4 years ago.

Hi Dr. Collins,

I had another ultrasound this morning. It showed me at 6 weeks 6 days with a heart beat that went up to 136. Would you be confident in saying that now we can be 100% sure that conception happened after the 29th of January and impossible to have happened after the Jan 14th encounter?

Dr. C., Board Certified replied 4 years ago.
Yes, absolutely 100% confidence that you did not conceive on January 14th. I would bet my house on it. Breathe a big sigh of relief and close that chapter completely. There is ZERO doubt about it. There is ZERO chance that there could be a 2 week error at this stage of pregnancy. I'm glad that it's worked out like this for you. Good luck!
Customer reply replied 4 years ago.

Thank you so much for your patience with me! You have really helped me through this pretty difficult time!

Dr. C., Board Certified replied 4 years ago.
Great, I just gave you the best correct answers as clearly as possible. I'm glad that it's gone well so far. I'll be happy to help you with any thing that comes up during pregnancy as well. I do appreciate your accepts! Thanks!
Dr. C., Board Certified replied 4 years ago.

Sorry I was just looking at the thread and see that I missed one of your questions asking for a link to the reliable research. Usually I get an e-mail telling me you are waiting with a question but I don't recall getting an email about that. If you still want it I can get it for you but it seems like its a moot point right now.
Customer reply replied 4 years ago.

Hi Dr. Collins,

I have been doubting myself again on the paternity of the baby. I realized now that I believe my hcg levels were too high when taken to be indicative of guy number 2. On 2/20 they were 2895 and 2/22 4486 (not taken 48 hours apart) but still high for someone who wasn't really even 5 weeks along at that point correct??

 

Customer reply replied 4 years ago.
Also, can you please show me the research on the non-invasive paternity tests?
Dr. C., Board Certified replied 4 years ago.
Sorry I've been on vacation. Thanks for your patience.
http://www.ncbi.nlm.nih.gov/pubmed/18949481
http://www.ncbi.nlm.nih.gov/pubmed?term=non-invasive%20prenatal%20paternity%20testing&itool=QuerySuggestion

The key in finding reliable research information is to avoid ".com" sites and focus instead on either ".gov" or ".edu" sites. So you will be looking for testing that uses the exact technology in the research studies.

I will be back from vacation this coming Sunday and can evaluate any test that you may be considering using in detail if you like.
Dr. C., Board Certified replied 4 years ago.
Tell me ore about your specific situation and I can guide you to the solution. Women in situations where paternity is being contested will need to use technology that will stand up in court. I can evaluate and recommend specific solutions to what is going on. On vacation it's a little hard for me to work on a small keyboard but if you let me know what you need I can figure it out. Explain more if you';d like to.