How accurate is the due date the doctor gives you when baby is scanned at first appointment? Really confused about when I'm due!

[Pinkflipflop]

I have thought I was 12 weeks pregnant but when the doctor scanned and measured the baby yesterday she said I was about 14w 5 d. I have very long and irregular cycles, so it's hard for me to be totally sure when I actually got pregnant. However if I could back 14 weeks and 5 days it was before my last period

How will I be able to find out for sure?

What the previous ladies have said, day 1 of your pregnancy is the first day of your last period. So if you've been thinking you were 12 weeks - counting from the date of ovulation, and the scan has put you at 14+5 then you're both right!

It is roughly 12 weeks since conception, but you are 14+5 weeks pregnant.

Mine was out by 3 days because I have endometriosis so my periods were irregular and I was peeing in a pot, and dipping some hormone indicator in it to tell me when I was ovulating. I did this for days on end before it showed up as positive so I was certain about my ovulation date.

I always came on my period 14 days exactly after I ovulated but never had 28 day cycle sometimes a 26 day cycle sometimes 35 sometimes 40.

When they dated me they dated me to 3 days before I ovulated which clearly can't be right, 3 days after maybe but not before. They went off their dates. I had an elective C section 1 week before their version of my due date so ds2 was actually 10 days early, covered in vernix!

I can understand them being out after you ovulate as sperm can live for days after ejaculation.

It does rattle you when you are told you are less or further along than you'd thought.

I'm convinced the edd told to me is a week earlier than my calculations but time will tell.

Ultimately, gestation is from 38-42 weeks - that's the normal range.

My EDD is 10 days off what we thought.
He seems by the scans to be spot on for this date but I think I may have ovulated twice that cycle.

pink its ridiculosouly confusing and I too have no idea on period dates as didnt have one for three months when fell pregnant!
My dating scan said - x date - then 12 week scan moved me a ahead a little, then a private 16 week scan moved me ahead a little but MW dont count that, but even now MW is measuring bump at what private scan said!
Its a bit of a worry for me, as due an ELC and worried about going into labour!

My 12 week scan was 6 days out from my own dates and also the dates of a private scan I had done. I just crossed their date off my notes and wrote my own in. This is my 4th dc and my babies always measure small for dates so I have extra growth scans etc and I also get choliostasis so the 6 days are important as with ds2 they went by their dates and induced me later than they should and he was lucky to be healthy.

I'm confident at my 28 week scan that the measurements will tally with my dates as they usually do.

Agree with the people asking when have you been counting from?

Disagree with the people saying early scans are accurate.

For medical reasons, with DS1 I had 3 scans before 14 weeks.
These went
My date 6w, their date 5 wk
my date 8 weeks, their date 6 weeks
my date 13 wk, their date 13 weeks

DS1 arrived 2 days before his due date by 3rd scan.

They might not update your EDD after a later scan, but if you are convinced about your due date, and you go over, you might wish to delay induction for a week if you go overdue by scan dates (due by your dates)

Congrats on your pregnancy

This has been a really interesting thread. I'm currently 37+2 with DC2 and was really shocked when my 12 week scan was dated at 15weeks! I was fairly sure I was between 13 and 14 weeks at that time.

DS1 was a big baby, 10lbs 5oz and I assumed that this one would be large too but I've always measured spot on for dates and I've had 3 growth scans which, at the last one at 36 weeks gave an estimated weight of 6lbs 3oz.

My query is simply how can all babies be expected to measure exactly the same in the first/early second trimester when there is such a wide difference in birthweights at term. Surely even at 13/14 weeks some foetuses will be larger than others? So, could my dates be right and this one actually be big like their big brother which was why they gave me an earlier due date than I thought? Obviously this doesn't matter at the moment but it will do when I get to 'term'

OP if you have long and irregular cycles then your dates will be calculated from 14 days before you conceived rather than your last period. Last period is used initially before the scan but goes on the assumption that you have a normal 28 day cycle and ovulate bang on day 14. Also as others have said it could have been an implantation bleed rather than a period, was it short?

Oy, I think it's because babies grow at a uniform rate in the first 12 or so weeks so they can use the size to date the pregnancy. After that growth rate varies which is why you have such a range of birth weights.

Even if you know the date you ovulated you don't know the date you conceived and even if you know the date you ovulated and there is only one possibility for the sex required you still don't know when the implantation occurs.

I was told by my midwife that estimates of the baby's weight later in pregnancy are subject to a 10% margin of error either way.

I was told ds1 would be small and turned out to by 9lbs 9!

Why have so many people been trying to explain the difference between the op's date by telling her that during 'weeks 1 and 2' of pregnancy she wasn't yet pregnant? She probably knows that already. It is irrelevant because the date they tell you at the scan is also according to the LMP system, so they were indeed telling her that she was two weeks further on than she thought. And how can that be, if as the op says, "However if I could back 14 weeks and 5 days it was before my last period" ?

I'm with the people who say the scans aren't quite as accurate as they are sometimes made out to be. I was told plus or minus five days (which still isn't two weeks)..

Mine wasn't splinters. Mine agreed with when i had ovulated but was 10 days later than my dates according to lmp. My cycle is 45 days long.

Splinters, and because she DIDN'T seemt

Also, it might not have been a period, could have been an implantation bleed.

Splinters - OP didnt know this- that's why we were explaining!

Will try to answer a couple of the questions that have cropped up.

Oy Babies grow at a very similar rate up until about 24 weeks ish hence why they can all be dated the same. The growth that causes the difference in birthweight happens later in pregnancy.

"nextphase" Dating a pregnancy before 11 weeks ish isn't very accurate which is why a dating scan is done at around 12 weeks (also it isn't possible to chekc some of the anatomy much before this time). So not unusual for 'early' scans ie before 10/11 weeks to be inaccurate.

"pink" I would be amazed if a scan was 2 weeks out on dates at this gestation simply because 10/12/14 week babies look so different regardless of size and so you just couldn't think a 10 weeker was actually 12 or whatever. I think it is more likely that you have either misunderstood how gestation is calculated or that it was an implantation bleed etc as suggested by others.

Also it is very unusual for the EDD to be changed dramatically after this scan, certainly unlikely to be changed due to the 20 week scan as it is much less accurate to date at this gestation. I'm not saying changes don't happen any hosptial policy will obviously vary.

balls.

Thanks everyone for the helpful replies to my question! So, looks like I am further on than I thought!

Just need the sickness to disappear now, could someone please tell it I'm now officially past the first trimester?!

Im confused when did I conceived who is the father i had sex with my bf on nov 2,3,4,9 withdrawal and nov 14 a guy popped inside me on my first ultrasound im measuring 6weeks and 5days on dec17 2017 pls help .

@Xephia it’s impossible to tell with the dates you had sex being so close together. Only a DNA test will give you an exact answer. But going by my calculations and the fact that the other guy did ejaculate inside you, I’m saying it’s him x