Gestational age vs other

Jane,

The date you got from the scan will be "time of pregnancy". It is more along the line of where you are in your cycle, seeing as it includes 2 weeks that you were not pregnant. So in reality you are actually pregnant 2 weeks shorter than what they say.

Honestly I would book the 12 week appointment based on your LMP. Even if you're not 100% certain.
I had 31-35 day cycles and usually ov'd around CD 18-21, and my scan dates always started coinciding with my LMP dates from 10/11 weeks.
The NT scan that gets done at 12 weeks can be done between 12-14 weeks, so even if you're not 100% sure and you book it for 12 weeks you should still be within the window. You will get a much more accurate measurement date at that scan. If you're really worried book it for 13 weeks and that gives you a one week margin of error on either side.

The doctors tend to always count pregnancy from LMP, so even if you are unsure of your dates and at your 12 week scan they tell you that you are now 12 weeks 4 days pregnant, that would roughly mean 12 weeks 4 days since the start of your LMP. But they will count that as the fetal age.
2 weeks pregnant however doesn't actually exist because it's the 2 weeks before you ovulate, but they still count it like that for whatever reason.

Thanks Ankie. And is that date from the scan the age of the fetus or the time of my pregnancy including time before fertilisation?

Hi Jane,

Using your last menstrual period as a way to calculate due date can be inaccurate. It assumes you have a 28 day cycle, and ovulated on day 14. Which a lot of women do not.

So if you have a 35 day cycle using your last menstrual period date (if you use the date when bleeding started, not stopped) you could be off by a week...


Go with the date the date you received with the scan

Ok, so even though she did multiple measurements the resolutions was too low to be spot on but then should I take the advice to use my LMS? The problem there is that I was not keeping proper track - the only reason I even remember when my last period was, was because they asked me at the hospital. I am fairly regular though, I just cant give a quantitative answer there.

I'm not going for a 10 week scan, only 12 weeks. That was my 8ish week scan (according to the sonographer!) and we did it because I took cortisone (among other things) before we knew I was pregnant and we wanted to see if it was ok.

I'm still concerned that I will go at the wrong time for the tests and we won't be able to find out if anything is the matter with the baby (I am very worried about the medicines I took in the first weeks).

What my gynae explained to me is that in the very early scans, when they measure, if their measurement is out by even a fraction of a millimeter it counts as a number of days. So the very early scans are not much good for dating. You will most likely find that by your 10 week scan the measurement results in dates much more similar to yours. And by 12 weeks they will likely be spot on. Book your 12 scan according to when you would be 12 weeks based on your LMP.

I have had 3 babies and only with the last one, was the scan date and my date more or less the same at the first scan.

What I always advise clients to do, it take the last possible date as your due date, so if they say you are 7 weeks, then it means that your due date is 2 weeks later than you thought. Use that date as you 40 weeks date. You might be spot on with your calculations. And then you will see your baby a bit sooner than your "medical due date".

I advise moms to use the latest date because we live in a country where docs like to start talking about inductions and scheduling c/s at 38 weeks. If your baby is really only 7 weeks now and you stick to your LMP due date, then that means that at "38 weeks" he will be only 36 weeks along and can be taken out to soon if there is a reason for you to need a c/s or induction before you go into labour. But if you use the scan date, and your baby needs to be born via c/s, you will have a better chance of baby being born on 38 weeks or if your LMP is really accurate, then he would be born at 40 weeks while the medical date says 38 weeks.

If your LMP date is correct, and you need a c/s at 38 weeks, but you are further along and go into spontaneous labour before your c/s date, then they will do a c/s on the day that you go into labour, so its not a problem that way either.

So you see, by giving yourself those extra 2 weeks, you are giving your baby a better chance to come on the day that he / she is ready to come.

Hope this makes sense, sorry if its difficult to follow....