Gestational age doesnt add up to when we had sex

[Lyndz123]

At my dating scan our baby measured 11 weeks 3 days but that wud mean we conceived 2 weeks after then at 9 weeks 3 days and that was a date we didn't have sex. We had sex after that date. Does anyone else's dates not match up?

The scan usually tells you when the fertilised egg implanted. This can be a few days after sex.

Scan dates are a very, very approximate indicator.

My DC2 was conceived via IVF. I know the exact date and time the eggs were collected and fertilised. I calculated my due date and the IVF clinic also gave me the same due date.

The scan dated my baby as being due 8 days earlier and the NHS refused to update my records with the real date.

Take your scan date with a large pinch of salt.

Mine are all over... I know when I think it was, doc disagrees according to dates size and growth . My only concern is that if I go into labour before they think it's 37 weeks they'll act differently, keep us in or whatever, even if it's not justified. Hmm.

The dating scans are +/- 7 days in accuracy.

I knew exactly when we conceived - appreciate implantation can happen a few days later, but my date was 5th of the month and the scan said 26th. NHS adamantly insisted they were right. Baby arrived on 2nd, almost 9 lb and huge and chubby. No vernix. The midwife thought the idea he was early was hilarious given he looked, if anything, slightly over. She also said they trust their machines more than women. I now take their version of events with a hefty pinch of salt.

My dates said 4th scan date said 22nd. DS arrived on 15th and midwife said lucky he came now as the placenta was looking old. she recorded him being born at 41+4 as per my dates not 39 as per scan date.

My dating scan made me 4 weeks more pregnant that I thought I was. We were REALLY trying to get pregnant so I'd done a preg test the month before and it was negative. And I'd had a period. I still don't understand it!

I'm not measuring very big now at 36 weeks so I think the dating scan probably was wrong.

Mine was over a week out too.

My scan has me due on the 22nd of November but my dates say the 8th!! And I know exactly when as my partner works away and we usually use birth control but didn't on one occasion as we were away and forgot it (oops, a happy accident tho).
So I am going off my own dates and not worrying too much as I think I will go earlier than what they think but know she will be ok because she is further along than they think. If that makes sense.
Most people I have spoken to say that scan dates are very inaccurate x

Sperm can live inside for up to a week. Ovulation can occur late or early. Implantation can take some time to occur. Conception is not an precise science.

It does surprise me that so many of you are so out on your dates according to the scan.

Being +/- 7 days different to your own calculations is normal as scans have a degree of margin for error.

But they are more accurate than people are making out. The development of a baby is pretty uniform in the first 12 weeks which is why they do the dating scan when they do.

If you go from your LMP however, you can easily get wildly different dates as you don't know when you actually conceived. Two women can start their periods on the same day and conceive that month but woman one can conceive on day 7 and woman 2 can conceive on day 29 and they'd actually be due 3 weeks apart but their LMP would suggest they were due at the same time. You obviously have to chuck in as well how long sperm live, how long implantation can take and you can get very different due dates to what you'd expect.

And at the end of pregnancy, it's worth bearing in mind that anywhere between 37 and 42 weeks is normal and some women naturally take more or less time than another woman with the same 'due date'. Mine were born at 37 and 38 weeks respectively, both good and healthy term weights. A friend had an emcs at 37 weeks and her baby was obviously 'early' and could have done with another few weeks on the inside.

Showofbloodystumps, we only had sex once that month as my husband was away for most of it. How long can sperm live/implantation take, because I would assume conceiving 3 weeks later, as my scan date would have required, would be an extreme outlier there?

It's possible I suppose, like I said I don't disbelieve it but I'm surprised. Baby development is fairly uniform for the first 12 weeks. A 6 week old foetus looks like a 6 week old foetus. They are very different to a 7 week old foetus and a 3 week difference would show up as a vastly different baby.

I know exactly when I conceived, know which day ovulation occurred and which day implantation occurred and was surprised that my scans were accurate enough to agree exactly to the day.

I guess if you say that the sperm can live in the ideal conditions up to a very maximum of 7 days, then it took a long time to implant (couple of weeks at the very most compared to another woman taking 6 days) and the scan can be out by 7 days either way, then I suppose it is just about possible to push it out by quite a way compared to when you actually had sex.

Can you remember what date you had sex on? I'm just intrigued by the disparity.

I knew the the date we conceived our twins, however, my 12 week dating scan made me 2 week further than I was. It did make a big difference IMO as our twins were born at 34 weeks (actually 32 weeks by my records).

There are all kinds of reasons for a wrong scan date. Mine was because the sonographer wrote down a different date from the one her computer told her, so human error.

The baby was apparently conceived when my husband was abroad 8 days before we had sex.

However, given that women are in charge of their notes I don't understand why confident women don't simply scribble out the wrong dates and put the right one.

My dates also do not add up to the scans. I know exactly when it happened as I was in hospital and we had not DTD for 2 months it was at a check up that we found out I was pregnant! By my dates I'm due in 10 days, by the scan dates am due in 3-4 weeks. I am, however, measuring "big" I.e my dates are correct. I have a new community midwife and she agrees with me after she had read my notes and seen my scans etc. we just go off my dates, but the hospital go off theirs.

Not now - DS is almost 5! But I was pretty concerned about the nuchal fold test's reliability if my dates were correct and theirs weren't. They reassured me that it would be fine, as I had the nuchal early by their dates and at the end of the window by mine. I didn't really worry after that because I couldn't see it made much difference, but then the midwife said women had said that to her before, and she believed them because of other indicators. It really interested me, because as you say I was flummoxed on how development could vary that much at that stage. I was wondering how they'd done the research into foetal development and how consistent it is, in fact.

I'm not sceptical about medical expertise. Get vaccinated for everything and ensure my child does, and so on. I know having access to the kind of medical care we do is miraculous in both historical and geographical terms, and I would be dead were it not for the care I had for an ectopic last year. I do trust medical advice. But this is one of those things where what you know and what they tell you is diametrically opposed. They said that implantation etc can vary, and I suppose 1 week for sperm survival plus one week to implant plus one week out on the scan is 3 weeks? But then the midwife said he was huge and plump and looked really well cooked to her, so... and I know I didn't cheat on my DH! Nor see any angels annunciating.

I suppose someone has to be the outlier, in the same way some women have to have the no bump or nausea/little movement/periods continuing that enables them to give birth without realising they were pregnant. But it did shake my faith in scans as a reliable indicator of gestational age. And from comments here, I'm hardly alone.

However, given that women are in charge of their notes I don't understand why confident women don't simply scribble out the wrong dates and put the right one.

My GP has a computerised version, my midwife has her own set, and the GP's ones are the "gold standard" all care is set by. Scans etc are arranged via that. I could scribble whatever I wanted but it wouldn't affect the antenatal care package, just the birth itself.

I had 2 early scans due to a suspected ectopic pregnancy. On the 1st June and there was nothing at all except a thickened uterus lining and my hcg read 230. 48 hours later it was at 550 and on the 15th June I had another scan and there was a tiny little bean with a beating heart. I was dated at 6 weeks 3 days which added up with the hcg levels etc. then at my dating scan 6 weeks later I was told I was in fact 14 weeks not 12 weeks like I'd thought. I had no idea how my baby could rapidly speed up when everything had added up exactly before - the hcg doubling exactly, the development on the scans etc.
At my 20 week scan my baby was measuring at 18/19 weeks but the doctor said we'll just leave your EDD as it is to avoid confusion. So I am apparently 24 weeks but really 22 weeks if that makes sense?

I just find it fascinating how it all happens. I suppose human error must also be considered (both from the sonographer and the woman miscalculating her due date). Of course plenty of women know exactly when they conceived, in fact I'm one of them, but I count myself lucky that the scans tallied exactly. It must be maddening for somebody to insist otherwise. I had quite a few scans with both pregnancies due to complications early on and saw the development go from pretty uniform in the first trimester to genetic factors (tall babies) kicking in after that. Although, I must say that I went for my nuchal scan and the baby was measuring really out but the sonographer said she wasn't happy with the baby's position or how my bladder was obscuring things and actually she'd rather I came back then next day for accuracy. Had she just gone with the measurements there, they'd have clearly been wrong so maybe that accounts for some of it too. They're so busy that I guess most of the time when all seems well, they work with what they have and allow the discrepancies to be just one of those things. One of my closest friends works in this area too and says that the extensive evidence does suggest uniform development in normal pregnancies in the first trimester. All that said, of course there are times when you simply do have to be the outlier. I've argued on here so many times that it's perfectly possible to take the pill at the right time every day AND use condoms with no problems or user error and still get pregnant. Because it happened to me. But people have no problem telling me I'm lying about it.

I think it's harder to tell at the end of pregnancy when the baby actually arrives, simply because some babies are born perfectly cooked, plump even at 37 weeks and some born at 40 weeks and still in need of a couple of extra weeks really. 37-42 weeks is the norm.

'but it wouldn't affect the antenatal care package, just the birth itself'

What care package?

I only had a scan at 12 and then 20weeks (which was 23 weeks due to being busy) with bloods, 4 drop-in midwife appointments on dates of my choosing and a telephone conversation with the diabetes midwife when I refused the diabetes test.

Same with mine

I have the same problem my due date is may 17 2024 days I conceived the 25 but I had unprotected intercourse the 26 that does not add up to my 5w3d ultrasound

gestational sac ultrasound at 5w3d does not match my dates I had sexual intercourse. My dues day is may 17 2023 I had sex August 17,18,26,27 that did ejaculate one on the 24 that had not even close to ejaculate and my conception date is August 25 . The dates are not adding up is it possible for my conception date to be off 1 day

I had an embryo transfer, baby has measured exactly 5 days ahead at every scan and I've had 5 scans. 6, 8 and 16 weeks private and 2 NHS dating scans (couldn't get measurements at 1st) I'm surprised that every scan has managed to measure to give exactly the same due date. The embryo must have either implanted early or the foetus grew super fast!
I'm not concerned as it's only 5 days but it does just show that even when you know exact conception date timings can be out.