Estimation Of Conception Date Via Untrasound

19 Replies
Skyeblue - August 10

Hello, Today I had my first dr. appointment. My last period was June 18, and I had s_x with my husband July 4, so I assume that is near my conception date. Based on the ultra sound my dr. made, he estimated me to be 4 weeds 2 days pregnat which would make the conception July 10-14th. I always make all important dates on my calendar; period, days I think I ovulate, s_x, etc. Could the dr. be wrong? I asked him and he said not to worry, just sometimes the results are such... Thanks for your comments


iemc19 - August 10

I don't think that sounds right - my last period - start date, which is how they date it - was June 15th, and I'm 8 weeks today..Ultra sound can give you a slightly better date but to put you out by so much of a difference is a bit odd. By your dates and such it sounds like you have a 30 day cycle but I would still think you would be dated as slightly more. If you're absolutely positive with your dates I'd query it...I always mark the dates too and with my last pregnancy the guy who did the ultrasound dated me as being 2 weeks less than I was..I argued the point with my specialist and he agreed to go on my dates...And as time went on and with an extra couple of u/sounds eevn the technician agreed on my dates finally...


Skyeblue - August 10

Hi, My cycles are 28-36 days, but I would say usually 32-33 days. Do you remember how or why the guy who did your ultrawound would be off by two weeks? Seems like my case... Have you had an ultrasound for your current pregnancy...if so when and what did it estimate? Thanks for your response


Tammy276 - August 10

That definately doesn't sound right, I think your doc. got things messed up. My last AF was June 22 and I will be 7 weeks preggo tomorrow, so you should be like 7 weeks, 4 days right now. His estimation just doesn't work out, unless he is telling you how far along you would be from the time you ovulated, but normall doctors will tell you how far along you are from the time of your last AF....You may just want to verify which way he is calculating.....Did they give you a due date? Mine is March 29th, so yours should be a few days before that.


Skyeblue - August 11

Hi Tammy, I went to two dr. now. One estimated my due date April 1, the other April 2nd. Both have different conception dates too. One said July 8-9 and the other said July 10-14! I know I had s_x on the 4th of July. I have read some differing opinions about the life of the sperm...I have heard anywhere from 2 days to 7!! Well if 7 days is in fact true then I suppose I could have conceived a week later than when we had s_x... What do you think? They say an ultrasound this early on is pretty d__n accurate; plus or minus 2 days.


Skyeblue - August 11

Also tammy, do you mean 7 weeks from conception...? They estimated me yesterday to be 4w1d (that was the first dr) and the 2nd dr estimated me at 4w 4d. My husband --the scientist he is : ) says you always count from ZERO, so when you think one week went by and you are entering the 2nd week, it is actually the 1st week. Does this make sense to does to me finally. Meaning if you count a week on say Monday then you would think the next monday would begin week 2, but it actually begins week one plus days. So the following Monday would be week1 and 2 days, or 9 days...


Skyeblue - August 11

Last question you have regular cycles?


iemc19 - August 13

Hi Skyeblue - the guy who did my ultrasound never gave a reason for his dates - normally an ultrasound is really accurate but I knew my dates and I'm very regular - and I know within 2/3 days that I've conceived!! My sizes must simply have been small and as I progressed the baby grew to compensate for the start...? I would aslo say that I've grown used to not taking ultrasounds at face value...My daughter - previous to that pregnancy was born 4 weeks early..I had started to develop pre-eclampsia and they were concerned about her size - so 2 weeks before she was induced I had a sizing scan and they all agreed she was a good and healthy 6lb+..When she was born she weighed only 4lb 15oz. So they were well out... I've never heard of sperm living longer than 3/4 days - but I could be wrong. And they always date from the first day of your last period and although you might have a slightly longer than average cycle I don't think its that big a thing - again no expert... I would double check everything with your dr and get him to explain why he has dated you the way he has, especially when you have specific dates..Don't let him fob you of! Ask for a proper explanation...And then I would also be asking for another scan - but ok I'm in the UK and I don't pay for these things, maybe easier said than done.... And this time round - I'm just beyond 8 weeks and I don't get a scan until 12 weeks here.... Good luck...


Tammy276 - August 13

Skyeblue, I normally have really long cycles, this time around I happened to ovulate 2 weeks early. I use the Clearblue Easy Fertility Monitor so I know exactly when I ovulate...Your doctors dates still don't work out....How long are your cycles? When they calculate your due date and how far along you are, they calculate by a__suming you have a 28 day cycle, ovulating on day 14 of that that alone can change your dates off by a few days, but normally only a few days unless you have like a 60 day cycle or something...Either way, your doctors dates don't work out, and an ultrasound this early really isn't that accurate for that reason, it is really early yet and your baby is growing fast...I've heard of some girls getting one done and measuring at 5 weeks when they should be 7 and the next week going in and measuring at 8 weeks, so I would wait because honestly, your due date should be before mine, your last period was a couple days before mine, so there is no way I can be 7 weeks 2 days, and you are only going on 5 weeks, it just doesn't make sense. I would get another u/s done in a week or so and I think you will see a difference. Yeah, I know about the counting thing, 2 weeks, 5 days and so on......this is my second baby so I know all about it!! The first time around I drove myself nutz looking at the calander every single day thinking alright, to day I'm 6 weeks 5 days and so made for a LONG 9 months!!


Sonrisa - August 14

You could have had a long cycle...My last period was May 8th...we ovulated the week of June 28th....I think we conceived some time between June 28th-July1st. We were very active that week. We are now 9weeks and 4 days pregnant. The u/s that they did on me said 6weeks and 4 days when I did it three weeks ago. They put down due date of March 22nd. Did he give you a due date? I have read that most u/s during the first trimester are pretty close..only days to one week off the actual day.


mistybuck - August 16

i am having the same problem, my last period was june 25, i thought i would have gotten pregnant around july 4 also but according to the ultrasound and blood work i ovulated very late and got pregnant when it was almost time for me to start again like on the 21 of july. I would like to know this also.


momofboyz - August 16

I am in the same boat. I had an ultrasound yesterday which would be around 9 wks. for me. My last period was around June 15th give or take a day or 2 but I know it was before the 17th because that was my son's birthday party. I had s_x on June 23rd & 25th. And I think we may have had s_x on July 1st (but I am not sure if this was that weekend). Anyway my ultrasound yesterday showed 8 wks. I have to go back next week to see if the pregnancy is progressing. The doctor seemed positive since we saw the baby and hb it is just that my dates are off. My cycle is usually around 30 days.


iemc19 - August 16

Hi Momofboyz - ur dates are much the same as mine - last period was June 15th, 28 day cycle flat, conceived on the 29th - positive about that cos I get symptoms within 2 days - queer but have done with every preg...this will hopefully be my 4th child..but i've also had 2 m/cs where I had the same post-conception symptoms...Anyways - I've been dated as being 9 weeks tomorrow....Your dates work bar a day or 2....for a 30 day cycle...What due date did they give you....I'm March 23rd...Maybe your next scan will alter it again by a couple of days.... I have to add that I haven't had a scan yet - I'm not due until I'm 12 weeks - maybe I'll have to argue my case then again!!!


Skyeblue - August 17

Thanks for all your responses. I thought that an early ultrasound was used to confirm pregnany AND estimate age of fetus NOT based on the last menstrual cycle. I am I wrong in a__suming this. I was told the embryo grows 1mm per day and therefore estimating age is usually not more off than 2 days. Has anyone heard the same or different...?


babytwo - August 17

I have been doing a lot of research on this subject this week. I had a SCAN on Tuesday believing to be 6w5d but to be told I measured 5w6d with no heartbeat. My Dr told to expect the worst and I go back for a SCAN next Tuesday. I was intially devasted however now somewhat postiive after what I have read and positive stories from others who have received the same advice as me. Firstly a number of sites I have visited state the optimal time to date is at 8 weeks. Prior to 7 - 8 weeks dating can be off by up to 7 days depending on experience of operator and accuracy of equipment. I have read that whilst one operator may suggests 5wk 3 days another operator on the same equipment may suggest 5 - 6wks. Also no heartbeat is expected to be seen prior to a 5mm measurement. 1mm a day is the suggested growth however not until about 6 - 7 weeks from LMP which is why 8 weeks is the ideal time to date by way of ultrasound. Many women have not seen anything or only something small at 5 weeks simply because it is too early. Another thing to consider is implantation. Whilst two women may be on the cycle implantation date may vary up to 5 days. Although dates are determined by LMP a 5 day difference in implantation can greatly affect subsequent ultrasounds between the same two women. Myself I am remaining postive yet still cautious. I hope these words are rea__suring to others on this thread.


dmk - August 18

babytwo- That was great info!!! Thank you!!!


Skyeblue - August 18

babytwo, thanks for the info, very interesting and thought provoking! please let us know how your next ultrasound goes. i hope all is well with you. i have an us scheduled for 8 weeks. will let you know. xx



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