When is a twelve week scan? Not a trick question...

[TommyTomTom]

Hello all,

First-time expectant Dad posting here… Any advice much appreciated.

Got a question about the 12 week scan that you might be able to help with. The question is “When is the 12 week scan?” I guess the typical answer is “12 weeks” but that doesn’t really help me for the following reasons:

As I understand it, the pregnancy is measured from the first day of the last menstrual period. Okay, got that. No problems.

So the first day of the last menstrual period is 0 weeks and 1 day into the pregnancy (officially). But this is also considered the first week of the pregnancy.

To continue this logic: after 7 days, or ONE week, a woman is starting her SECOND week of the pregnancy.

After 14 days, or TWO weeks, a woman is starting her THIRD week of the pregnancy….and so on.

So, the question is:

Does the 12 week scan occur after 84 days (or twelve weeks) or does it occur after 77 days (which would be starting the twelfth week of pregnancy)?

To confuse matters, does the 12 week scan actually occur 12 weeks after conception, which would be around 98 days into the pregnancy (which would also be after 14 weeks or starting the FIFTEENTH week)?

I’m really confused!

I really only want to know this because I would like to take my wife away for a last holiday for us before the second -trimester and I want to avoid booking it for the week when the NHS are likely to send through the appointment for the 12 week scan/chat.

Heeeelp!

Generally they double as a nuchal scan and those have to be carried out between 11 weeks, 2 days and 14 weeks, 1 day. Exactly when your PCT is likely to choose in that period is anyone's guess...

IME, the "12 week scan" can happen anywhere between 10 and 14 weeks. Same with the 20 week scan - could be 18, 19, 20, 21 or even 22 weeks. there;s no knowing when she'll be called in, TBH.

The scan should be 12 weeks after first day of last period or 10 weeks after conception. There is quite a narrow window for the scan to happen as they need to take nuchal fold measurements and blood tests before 14 weeks. Depending on how your wife feels, maybe wait until after 14 weeks when any sickness and tiredness feelings start to pass (usually).

If your wife is suffering tiredness or nausea or any of the other things that make you feel like shit in the first trimester, then it may be a better idea to go on holiday in the second trimester when a lot of women feel much more normal, with energy levels increased and (hopefully) any morning sickness will have got better too.

why so important to go on hols before the 2nd trimester? Usually women feel best (less sickness, but not huge yet) during 2nd trimester, so that is usually best time to travel. 16-18 weeks maybe a good bet.

Sorry all, should point out that I meant to say that I want to take us away during the second trimester - not before!

It does seem that the actual date the NHS send through is not going to be exactly the 12th week anyway so perhaps the question is now academic.

So count that as 15-19 weeks after LMP. Usually a scan about 20 weeks you don't want to miss, either. Next window approx 23-27 weeks.

12 week scan is 10 weeks after conception.

Thanks, though!!! All very interesting.

also she might need to go back to be re-scanned, I did with both my 12 & 20 week scans as baby was lying awkward for the measurements.

Congrats

I find it easier to figure out weeks by starting at the due date as 40 weeks, then counting backwards.

Your calculation of dates in your first post felt very confusing to my not mathematically minded brain.

I agree with Nosy book the holiday somewhere between 15w0d and 19w6d or somewhere after 23w0d. Those should be reasonably clear periods scan-wise (assuming that you are in an area that does "12 week" and "20 week" scans historically some have done one combined 16 week scan (this was supposed to have been phased out when I was having DC1 ten years ago, but was still going on in some areas (not mine!) when I had DC3 three years ago; don't know if it's still the case).