To ask for your help explaining this to my boyfriend?

[ufgh]

So, I'm trying to explain to DP about due dates and the fact they're calculated from your last period.
We know full well I conceived 2.5 weeks after that as we hadn't slept together for ages before that.
So now he's confused that we slept together and conceived say 12 weeks ago but baby is measuring 15 weeks.

How do I explain this?

It is really weird. Both our DC are IVF and the pregnancies are dated from before treatment was commenced.

Day 1 of pregnancy - day 1 of your period. The egg(s) start to mature in your ovaries.
Then the egg(s) continue to mature in your ovaries
Around day 10, you ovulate. This (approx 3 day) window is when you have sex
10-14 days later, if you are pregnant it will show up on a pregnancy test. At this point you are 3-4 weeks pregnant even though you had sex a fortnight ago.

Prior to the baby being born, when they say the baby is measuring 15 weeks - they mean the baby is measuring the same size as is expected of a foetus conceived 13 weeks ago, and assuming the mother had her last period 15 weeks ago.

They carry on with that form of conveying the info all the way to the baby being born.

I have a 40 day cycle. In my last pregnancy I had my period 11 weeks before the day of an early scan. But the baby was measuring 6 weeks. ie I had conceived the baby from sex that was had about 4 weeks ago. So even though my last period was 11 weeks ago my ovulation only happened 4 weeks ago, and the foetus was that size.

In this day with ultrasound and precise measurements, they could of course switch to actually using the age of the foetus rather than the traditional pregnancy lingo - but it's hard to change established habits and everything pregnancy related is tied to those dates. So dating scan is 12 weeks (when foetus is 10 weeks old), abnormality scan is 20 weeks, viability is 24 weeks, and so on.

There is no logic to it and it is confusing.

Of course it's logical - as several pp have said in days of old there was no fixed point to refer to other than LMP.

Otherwise you have two parallel schemes running alongside each other which is a hell of a lot more confusing.

You can agree to differ OP. Why is it important to you that he views it exactly the same way you do?

To be fair to him I think it's bloody annoying.

I know exactly when I conceived and find that I actually have to quote a week that I know it isn't annoying. The Biologist in me just wants to scream.

I understand why they do it as most won't when they conceived but I can understand why it might be a bit confusing.

He's still confused. He just isn't grasping that on the day you actually conceive, baby measures 2 weeks/you're 2 weeks pregnant!

Well, tbf to him, he is right. It doen't make sense in general conversation or thinking about measuring things. I agree with him. Personally, I can just go "well that's a daft and confusing system" and move on, but I know there are lots of people in the world who like to relly understand everything before they can let it go.

You can agree to differ OP. Why is it important to you that he views it exactly the same way you do?

Because if he tells the hospital that she is 35 weeks when she is actually 37 weeks then they will make the wrong decisions for her and their baby. This isn’t the op’s special way of looking at it - it is the medical professions way of looking at it.

Sometimes with children you just have to say “Because it just is”

I suggest you start practicing.

He's still confused. He just isn't grasping that on the day you actually conceive, baby measures 2 weeks/you're 2 weeks pregnant!

Just tell him they add 2 weeks on to the start of pregnancy as they date it from the first day of your last period as usually they don't know the exact date of ovulation/conception.

Which is bullshit for all the people ttc and tracking, I knew the exact day of ovulation and the exact day of implantation.

There is nothing to understand.....its a convention based on the fact that the time of the last period is known, while the time of ovulation or the conception isn't.

Op...are you the one actually being a pita about it ?

Dont they date it differently in america like actually 2 weeks past the period

I agree with your partner. I was confused by it as well; it’s definitely not logical.

Can't you just say that the egg is maturing and waiting for the sperm so that is how the fetus ends up a couple of weeks already because the egg is already ripening. I thought i understood pregnancy well but now even i feel confused trying to explain it.

just get the dates in a due date calendar which will show you everything. This one has extra explanation too.

www.yourduedate.com/

Just to confuse him even more tell him in Korea a baby is 1 year old when born lol #mindblown

@IrishGal21 How do they work that out

It's only a rough guide anyway according to my 12 week scan I conceived several days before I ovulated. It's based on averages based on research studies, many people who have ivf ie absolutely certain when the baby was conceived are given adjusted dates. have you explained that babies fairly arrive on their due date yes otherwise he might be in for another shock

^rairly

Tell him sometimes systems are arbitrary. In the UK, I think every horse has an official birthday of 1st January to make the administration of year-based horse races easier. In England, I think children are allocated to school years based on their age around 1st September even though that means you can get two children in a class with 364 days difference in ages. Some things just are.

No, it's not different in America, it's the same.

It's referred to slightly differently in Germany. When you're (say) 6 weeks + 3 days, you're considered to be "in the 7th week" which confused me a bit. But the actual dating is exactly the same.

It's just because pregnancy dating predates scans (let alone scans which can measure a baby for dates) and ovulation monitors and such. If they'd changed the way a pregnancy is referred to it would become confusing in literature etc, and you'd end up with potentially risky situations if a mother thinks she is 2 weeks ahead or behind where she is. It doesn't do any harm to have it be slightly illogical, so the benefit of changing it isn't high enough to justify the hassle and potential risk.

Maybe he doesn't realise you can only conceive on about 3-5 days each cycle? It makes more sense when you understand that part IME.

IrishGal Google also tells me that your age goes up on 1st January every year, not the day you were born.

So in Korea, a baby born on 31 December is actually considered to be age 2 from when they are one day old. That must make buying clothes for babies and toddlers bloody confusing.

Tell him to Google it.

Personally I think it's a bit stupid. How can you be pregnant before you're pregnant? Olden days, yes, count from LMP but why not subtract 2 weeks?

When I conceived my youngest I was having 50 day cycles so the LMP date was really inaccurate. I knew exactly when I'd conceived as I was tracking (was about to start IVF!) Despite this being on notes every midwife/ sonographer asked for LMP and reacted with horror, asking why I hadn't made an appointment before, as it sounded like I was 5 weeks more pregnant than I actually was!

The EDD is calculated by adding 40 weeks to the date of the last period because that is the one thing that is usually known to a degree of certainty.

If the calculations were based on conception date, should that be known to a degree of certainty, the gestation period would be 38 weeks.

The convention is accepted and used in medical circles even though it is in fact wrong and the fetus is not actually 12 weeks old when we say it is. It has been 12 weeks since the point in time that convention states is the start of pregnancy.

It is slightly crackers......