Dating at first scan

[bluemoon2468]

I'm currently 5+2 based on my LMP, but because I was tracking ovulation and felt my implantation I know it was all a lot earlier than average. I also got a CB 3+weeks when I should only have been around 2 weeks according to my current dates. I think when I go to my first scan at 10 weeks there's a good chance they're going to give me an earlier due date.

I was just wondering, if the due date changes based on fetal measurements at the scan, then does that change all of the dates for your pregnancy (end of 1st trimester, 20 week scan appt etc.) or just the due date? And do the dates based on measurements tend to be more accurate at predicting when the baby will actually come?

As far as I remember the dates would all change with how far the sonographer says you are along. Surely it'll only be a week or so difference though?

Same with when the baby will be born, it will likely be between 37-42 weeks.

Yes, they will go from your LMP up until the dating scan, and then dating scan will then set a new timescale. I wouldn’t pay much attention to the CB thing - it’s more of a fun feature than a diagnostic tool - but your tracking ovulation obviously is more accurate. But it can’t be out by more than a few days?

Yes. They brought all of my dates forward by 5 days.

I think it's out by almost a week! But yeah in the greater scheme of things it doesn't matter too much! Was just wondering 😊 thanks!

Yes all the dates would change I went for my first scan where I thought I was 13 weeks but I was only 12 weeks so your dates shouldn't differ by much

We had our 12 week scan last month, and they brought our due date forward by 5 days. Prior to this we had been given 3 different dates anyway, but the date given at 12 weeks scan is what is kept 😊
Congratulations on your pregnancy x

Dating by scans always seems a bit inaccurate and therefore potentially risky.
I found a due date calculator online that went by your LMP but also looked at your cycle length as an indication of when implantation actually happened.

I was measuring further along at my 12 week scan but my hospital wouldn't change my due date unless it was 10 days out either way. I was only measuring 5 ahead so they have kept my due date from LMP, now 28 weeks and still the same due date.

it’s only really an issue if you are overdue/early and being encouraged to accept an induction for whatever reason but you feel like the baby isn’t ready yet and you don’t feel that the risks are outweighed by the benefits in your situation. If they are going by dates that you don’t think are quite accurate then it’s a bit of a pain being under that pressure. But there’s a long way to go yet. I was bumped forward by 6 days with my son and he was 3 days overdue (which for anyone who went to 41/42 weeks doesn’t count as late at all!)

I did look at another way when they brought my baby's due date forward. From my point of view, having had 2 miscarriages, it meant that firstly I wouldn't have to wait so long until my next scan, and secondly it brought the date of viability forward by 5 days. I was pleased rather than worried about it. I did go over my due date by 10 days in my last pregnancy though.

I know they can make mistakes, but the sonographer said at that stage, there isn't a lot of room for ambiguity. Plus even if you know exactly when you had sex, sperm can live for up to 5 days. No idea how reliable ovulation testing is though.