To wonder if dating scan could be wrong?

[Beansprout30]

Second child was due 8 days ago, I know it's perfectly normal to go overdue but I've had zero signs that baby is going to come anytime soon and today it crossed my mind if my due date could have been wrong?!

When I went for my 12 week scan we were told I was actually 16 weeks gone, which was a bit of a shock but not impossible, however that first month we ttc, I got a negative test and full on period.

Has anyone else ever thought their dating scan was inaccurate?

I thought all of mine were inaccurate purely because of the size of my DC . The smallest was 9 lbs 6, biggest 10 lbs 3. No GD involved and I only went three days over with all of them (in fact only reason it was only three days was because I had a sweep).

I don’t think dating scans are often wrong though. If they measured you at 16 weeks, that is a massive difference in size from 12 weeks. They would have to be fairly incompetent to judge a baby’s size THAT wrong at that stage. You probably just have a very happy baby in there, it’s very common to go way over especially with first babies.

With my older kids they were still test running scans really and they didn't always change your dates. My sons due date cane and went and he was 10 days late, but he actually arrived on the date the scan gave.
2 years later my daughter's due date came and went, she arrived 14 days late (4 days after the scan prediction)
I would also ad that for me my periods were correct but a 5 week cycle, and during the period I was overdue I had no signs of delivery even after 4 sweeps.
I would perhaps mention to your midwife and have a well being scan requested?

Probably should have added this is second baby and first was four days early

They're generally pretty acurate, but can be wrong i think - freinds of mine have been absolutely convinced theirs were wrong (dates of conception pretty clear and whatnot).
However, i went into labour bang on 42 weeks without any sign it was coming. Went to bed the night before i was due in for an induction pretty sure that would happen and woke at 5am when my waters broke and i was in active labour within 2 hours, baby in my arms 2 hours after that.

Yes. My son was related at two weeks further along at my twenty week scan. I think this was wrong - I had an ElLCS at 38 weeks which I now think was 36. He had breathing difficulties and spent time in SCBU.

Just a hunch but I've always been suspicious.

There’s a huge difference between 12 and 16 weeks though. I can’t believe that could be wrong

I'm positive ds2 date was wrong. He was huge at 9lb 14 but I had to have growth scans and everything. I had no gd or anything. He was born via elcs (due to previous failure to dilate with ds1) and the surgeons and drs where all like.......he is so huge are you sure your not over!?!?

I was 12 days “overdue” with my daughter, who was induced in the end because of my age (v late 30s).

Through the pregnancy there was a lot of concern about her being a very low percentile in size (2nd or 3rd), despite growing consistently. Kept being told she was “two weeks behind” in growth.

When she came out she was covered in thick vernix and the first thing the midwife said was
“that’s not an overdue baby”. She was unusually long and skinny (still is!), and my guess is that this somehow threw the calculations out, as dating is (as I understand it) based on average measurements.

You said your first was 4 days early, so was the scan correct?
I just remembered with my dd2 I was induced at 37 weeks due to leaking waters, but when she was born she was 34 weeks gestation and need SCUBU. So I guess yes they can be out, but generally they are fairly accurate.

I'd just like to say that my identical conceived-at-the-exact-same-moment twins were given different dates at the scan. About a week apart, I think!

However the sensible nurse picked one and went with that.

It's all to do with the way they measure them on the screen. You see the way they pull the line a millimetre outwards and the date changes by a week!

Interesting to read others experiences. I could see myself at the first scan baby looked bigger than my first at 12 weeks but I was convinced I wasn't pregnant that soon what with having a full blown period (I know that's not impossible though). Will be induced at the weekend if baby doesn't show before, id rather wait but if due date really is correct I don't want to risk going too far over.

I did wonder if my first dd's due date was correct as according to that one, we must have dtd during the week we never did!

I think ultrasound measurements can be up to 15% out one way or another so that gives some space for inaccuracies.

DD1 was definitely dated wrong. I know exactly when she was conceived with absolutely no chance of another date, yet she was dated as conception being 5 or 6 (can't remember exactly now) days earlier. The other way around could make a bit more sense with sperm hanging around for a few days, but not this way. I also then spent the whole pregnancy being told she was measuring a bit small...
DD2 I was equally very sure of dates and the scan dated me a couple of days earlier.

2 - 4 weeks out seems like a lot though?

I think the dating scan with my second was wrong. We were trying, I know, I ovulated around the 12th. I also know we only managed to have sex one that month, on the 11th.

When I went for my 12 week dating scan, I was confident I was 12 weeks and about 2 days. Scan put me back to 8 weeks 4 days.

I ended up being induced at 36 weeks as my placenta stopped working, but my son was born 8lb 9oz.

I was so confident with my dates, and with my son being so big and quite early I’m convinced the date was off.

Mine was 2 weeks out. I knew the date my baby was conceived as DH was working abroad. They put me a week later, I argued but let it go. The baby was born at 39 plus 10 days weeks but it was really 39 plus 17/8- he was enormous and ended up being quite ill.

At DS1's 12 week scan we were told that I was a week further than I was. Funny that, seeing as DS1 was an ivf baby and we knew the exact date that he was made. The midwife refused to believe that the scan could possibly be wrong. Guess what, I went a week over their date, DS was born one day after what I knew was his actual due date.

My eldest was 8 days late and 10lbs 8oz! However his first scan gave an edd of a week before this, meaning he could have been 15 days late. For his size this seems more reasonable.

they can be wrong. I knew with absolute certainty when DS2 was conceived and had some very early scans. Towards the end of the pregnancy he was measuring bigger than expected and I had an idiot doctor (at a different hospital after a scan) try to condescendingly explain to me how they dated by scan measurement and how I must be wrong. Fortunately my notes were very specific, and he was finally talked out of inducing me.

Scans decrease in reliability the further along in the pregnancy the mother is.

The 12 week scan is fairly accurate and where I work we advise that there's a possibility of 3 days either side.
There's a huge difference when scanning at 12 weeks compared to 16 and not just in size.

Mine was 16 days over due wit h no signs of coming. I wasn't even dilated at all even after being induced which failed. Had to have a csection

We moved hospitals with our twins as the local hospital didn't have the facilities for high risk identical twins. We had a booking in appointment at the big hospital the day after having the profit one at the smaller hospital and was dated almost 2 weeks different!!! I'm pretty sure the actual date was in the middle but nearer to the 2nd estimate so yea not an exact science. They were born just shy of 36w and looked more like 34/35 according to the consultant who delivered them...that would fit with my estimate.

My dating scan with my twins confused the life of me, I know my period started on the day we went on holiday 17th feb, was given a due date of 9th dec.

If your measurements fit in at the normal the 20 week scan then it won’t have been far wrong. Most babies are all very much a similar size at 20 weeks.

The difference between a 16 week baby and a 12 week baby is huge. I am pretty sure the sonographer would have know what they were doing.

It's bad if you are correct. How many women would go through having to be induced needlessly because the sonographer got their dates wrong??
I always said with DS - he will neither be late not early but will arrive precisely when he means to. A bit like Gandalf

That should say late nor earl

Mine is definitely wrong by at least four days (literally couldn't have conceived as early as we did, as didn't have sex until four days after it was dated), but there's a big difference between four days and four weeks! Sonographer was insistent on the date being right and I just shrugged and said well it isn't, because it's impossible (obviously four days later might have made more sense as don't know when exactly egg/sperm combined and implanted, but literally impossible four days earlier unless immaculate conception!), but ok....! He did say the 12 week scan was plus or minus 5 days though as well... Four weeks is quite a different kettle of fish though!