Need help with conception dates!

[Ruby46]

Hello, new to this so hope I'm writing in the correct place! I'm a little confused and would like a little help on when I possibly conceived. Unfortunately I don't know when my last period was. I had intercourse on 16th December and 26th December. On the 1st January I had what I have been told was an implantation bleed, it was slightly heavier but definitely not a normal period. I had a scan last week and was told I am around 8 weeks 2 days. Obviously considering the scans can be a few days out, would I have been more likely to conceive on the 16th or 26th as I had the bleed 5days later?
I hope that all makes sense. I have asked my doctor etc but they don't seem very willing to help me.
Thank you

Things you need to consider,

Not everyone ovulates day 14 of their cycle.
Sperm can last for a few days after sex so can fertilize the egg a few days after sex.
Due dates account for 2 weeks pre conception as they go from your first date of your last period. So at 4 weeks your baby is actually 2weeks. (I know it is nuts). It is to allow for early and late ovulation etc.

The conception date would be largely irrelevant as you don't know your LMP as they will go with the due date given by your scan at 12 wks.

However if you need to know because you had sex with different people (just saying as this can sometimes be the case) then what date did you have your scan and what was your gestation on that date? Count backwards, then you can get a better idea of when you may have conceived, taking into account the first 3 points I made.

I had a scan last Thursday 19th and she said I was around 8 weeks 2 days, I also had another scan that day due to other reasons and she also said I was around 8 weeks. This is what makes me think maybe it was the 26th that I may have conceived?

Its best to wait until your 12 week scan, my early scan dated me at 8 weeks 4 days, which would have made me 12+1 at my 12 week scan, but when that came around I was dated at 12+6

If you were scanned at 8+2 on the 19th of this month, this puts conception at around January 6th give or take.

Did you have sex again after the 26th of December?

I was going to say the same as Showy, your conception date is most likely early January.

I had sex on the 6th January which was the day I stopped bleeding (been told this could have been an implantation bleed) had sex again on 10th. When I asked at the scan she said it's unlikely I conceived early January as I would only have been 6 weeks on my scan. Thanks for your help it's all very confusing to me!

If the scan was 100% on the money, your date of conception is January 6th. Your sonographer seems confused. 8 weeks and 2 days puts you at 6 weeks and 2 days since conception. She seems to be mixing up how we date pregnancy (from 2 weeks before ovulation, around the time of your lmp) and when conception occurs.

Sounds like the 1st of January was your period and you ovulated early in your cycle.

If you'd conceived on the 26th of December, you'd be well over 10 weeks now and your scan suggests you're only just at 9 weeks. If you'd conceived on the 16th, you'd be 12 weeks now.

If you concieved on the 16th you would be around 12 weeks by now, if you concieved around the 26th it would put you at around 10+4 (give or take, as sperm can live a few days) this sounds confusing but 2 weeks are added onto conception dates, that is even with scans done, as they take the extra 2 weeks into account aswell. I.e im now 28 weeks which is equal to around 26 weeks since conception. Your dates they gave you do currently match up with the 6th of january at the moment, but as apple said earlier scans can be quite off sometimes, mine was 5 days out compared to my dating scan 3 week later. I would wait for your dating scan but even then its not exact. Its all very confusing.

Cross post with showy lol

Thanks all for your help. Think I'm going to give them a ring and get them to explain it to me too as what you guys have said is different to what both the sonographers said. Maybe talking to someone else there will help.

When are you seeing your midwife again? They are the people to ask really. Do you have your notes from the scan?

Is there a particular reason why you need to know exactly when you conceived or is it curiosity? Do you have your 12 week scan booked?

That's a lot of questions. Sorry!

No worries I spoke to the clinic today and asked them if this is how they worked out how far along I was. She said as I didn't know exactly when my LMP was they literally look at the scan and depending what the measurements are that is how many weeks I am (which last Thursday was 8 weeks) She said they don't plus two weeks etc. My scan is booked for the end of march I think I'm going to be a little further than 12 weeks by then. I am just curious to be honest and the more looking into it I done the more totally baffling I found it! My doctor hasn't been much help at all and I wasn't really sure where to go.

Are you in the Uk? I have been pregnant a few times in a few different places, plus been a MNer for 10yrs. Never have I heard of pregnancy being dated from conception in the UK. Plus, if they are leaving your dating scan that long, they are possibly going to end up missing the window for nuchal testing.

Unless you are talking about one of these private viability scan places?

Put it this way, if they dated you from conception, you are now 11 weeks and need your dating scan earlier than a month's time.

As the ultrasonographer says, if the scan says 8+2 you were 8+2 give or take. The measurement at 12 wks will be more accurate. A few days either way wont make a difference to your nuchal if they have booked you in when they think you need your nuchal scan. So you can relax! (I am a former mw and have seen this many times!)

Putting your scan data in this calculator gives you a conception date of Jan 5th.

I'll give you an example op, my lmp was 1st Nov. I did 8th and 10th (i ovulate early). My pregnancy is dated from 1st Nov, y due date is 1st august based on 12 wk scan measurement. So obvs I wasn't pregnant on 1st Nov as i started my period! The scan sizes agreed with my dates give or take a few days (to allow for early ov and short cycles))

Jmojo, read the thread again. The sonographer is describing her as 8+2 on Thursday last week but the op says this is 8+2 from conception. So 10+2 in terms of dating the pregnancy traditionally. Which implies she is 11 weeks today. Waiting another month at least for her 12 week scan is not right.

Somebody, somewhere has made a mistake. Either the op has misunderstood or there is a discrepancy between what this clinic thinks and what the person booking the 12 week scan thinks.

Scans go on measurements for the gestation of the baby, as the op says the ultrasonographer said 8 wks it is 8 wks conception date has nothing to do with it. No plus 2 weeks needed, it is on babys measurements. Measurement scales were created based on women knowing their Lmp. So when they were created they inherently already account for the 2 wks. Ie women came in knowing from their lmp they were 6 wks/20 wks/34 wks. Measurements were taken and charts were created based on averages of all of these women, so we could know what the crown rump length would be at 8 wks (inc the 2 wks post lmp and pre conception) . So now when they get certain measurements they can look and say 8 wks. No need for the extra two wks to be added, as the charts were created with them as part of it!

Jmojo, you are misunderstanding me/the thread. I know how pregnancy is dated and why it is historically 40wks from lmp. As I have explained, you have explained and others have explained, 8 weeks and two days pregnant is 8 weeks and two days pregnant. BUT the op wanted to know when she conceived. We explained that it was approximately 6weeks and 2 days before the scan. The op has said a couple of times that the sonographer has disagreed with this and that if she conceived in early January she would only be 6 weeks. This is WRONG. There is a wire crossed somewhere.

I am 8 weeks tomorrow, my last period was right at the start of January, I conceived around the 14th January. If you're a week ahead then you would have conceived around the 7th jan. Sperm could not survive from the 26th December.

WhereIsMyFurryHat but when I spoke to the hospital yesterday they said I am 8weeks end of, there's no plus two weeks etc. She said it's measuring 8 weeks so that's how far I am :/ I also had a shorter period that I've been told could have been an implantation bleed that started on 1st Jan and ended around 5th-6th

Its getting hard to explain now lol. They have said that to you because that is how many weeks you were given on how we date a pregnancy here in the uk, so yes you were 8/40 weeks pregnant BUT that still doesnt mean you concieved 8 weeks ago. Im 28 weeks pregnant I concieved 26 weeks ago but im still 28 weeks because pregnancy is not dated from conception in the uk. If you put how many weeks u are now into any conception calculator it will still give you january as a conception time. Its just how it is and its same for everyone in the uk. And as been said above if you had concieved in december you would have been "dated" as been well over 10 week by now. Its confusing but thats how it is.

Absolutely mumof3. If your LMP was 1 Jan (4-5 days is a substantial bleed be it shorter than you are used to or not) then you would have been 7wks on your scan date, (which is not out of the potential error at that stage with a scan, the 12 wk is the most accurate).
However it would put conception between 6-10, which with an early ovulation is possible. Hence the difference in the gestation as you would have ovulated a week earlier than most people do - so 7wks becomes 8wks!!

I would say most likely your LMP was 1st, you ovulated at 7-10 days rather than 14. You had sex then and hence you conceived. As you ovulated early your date was a week further on your scan hence you were 8wks and not 7wks with an LMP of 1 Jan.

Ruby, the confusion is coming from the difference between when you conceived and when they date you from. I can see why you are confused. If they specifically said you can't have conceived in early January as that would make you 6 weeks, then they are wrong. We don't date pregnancy that way. Is this the UK and an NHS scan?