How long is a pregnancy actually? AIBU to be so confused at this?

[WhatTheActualFuuu]

Name changed for this because it's possibly the stupidist question in AIBU history.

I don't have kids (I'm on MN for the life advice and laughs) and I've honestly always thought a pregnancy is 9 months.

But then I see posters talking about being early at 38 weeks, and referring to being 40 weeks pregnant.. I thought a pregnancy was 9 months, so 36 weeks?

AIBU to utterly confused?

I know this is totally irrelevant to me at this point but I just cannot work it out!

I'm sure I worked out it was really ten months. Maths has never been my thing though 🙈😂

38 weeks from conception. But gestation is based on the first day of your last period so 40wks taking that in to account.

@WhatTheActualFuuu My pleasure

Oh, grow up! The OP is entitled to be confused because it's a lot more complicated than the number of weeks in a month.

FWIW, one reason it is so confusing is that we tend to confuse two things: what medics have figured out is a 'normal' pregnancy by looking at lots of examples, and what any individual person experiences.

Until pretty recently, women didn't know they were pregnant until they'd missed at last one period, and we couldn't easily track ovulation. So periods were taken as important information for dating pregnancies. For most women, the date of the last period is a good enough guide to roughly when you got pregnant. Then, you can measure things like the size of the foetus at 12 week, and that's quite a good indicator of how things are going, too.

There is lots and lots and lots of data showing what happens if a foetus is a certain size 12 weeks from the last menstrual period.

However, if (like my DP), you mess up the data by tracking your ovulation and going to a fertility clinic where they inject sperm into your wahoozie, you may feel you can be smug and tell the doctors their dates are wrong. You may even find that, at your 12 week scan, they tell you you are an impossible number of weeks pregnant (eg., they'll suggest your egg encountered sperm a week or two before that was remotely possible).

This isn't because doctors are stupid. It's because big data - data taken from millions of women and their foetuses - is still enormously useful in telling us how a pregnancy works, even if we no longer need to measure from the date of the last period. We're better off accepting that terms like '40 weeks pregnant' are a bit of a medical misnomer, than trying to reinvent the wheel and gather all that data all over again.

I agree overall SarahAndQuack. However OP explicitly said that she was confused because she thought 9 months was 36 weeks. That’s why people are pointing out that a month isn’t 4 weeks.

It's all irrelevant now anyway, or will be soon. Viability scans at 7wks are being offered at many trusts and they are used more accurately for early dating now. I had one at 7wks 6d (I knew the day I ovulated as mine is very painful) and DS measured exactly 7wks 6d.

At my 12wks scan he was measuring 2 wks ahead and did for the whole pregnancy. If they had used that date for my due date, and to indicate my conception date, my husband would've been very fucked off as he wasn't in the country two weeks prior to my actual conception date!

I don't think anyone is saying someone who hasn't been pregnant should know about the ins and outs of the period of gestation but it's perfectly reasonable to not understand how someone doesn't know how months work, it's got nothing to do with pregnancy

@SarahandQuack thank you, that makes so much more sense!

To clarify again, I'm fully aware that four weeks isn't a month. But 40 weeks isn't 9 months, as much as 36 weeks isn't.

And no, maths is not my strong point.

But it does seem a little harsh to jump on a badly phrased OP like I'm stupid - I'm not, but again, I've never had a reason to consider how long a pregnancy actually is and I don't think it's unreasonable to ask.

I have few dumb questions.
If you can tell the date of conception, do they still count from previous period?
What if you don't have regular period?

I think I must have missed a vital class in school, because I didn't realise that if you had a positive pregnancy test on Day 28 of your menstrual cycle, you're considered to be 4 weeks pregnant, even though you probably actually only became pregnant 2 weeks prior to that.

I only discovered this when I went for my first pre-natal appointment and was told I was 2 weeks further on than I thought I was - I was 35, so really should have known!!

@Rezie they still work from last period because that is what the computer can cope with then you go for a 12 week scan and the re date you there. Therefore you get a more accurate date to take into account irregular cycles. Both my pregnancies were put forward 6 days, dc1 was 6 days late and dc2 was 11 days late according to scan. I hadn't ovulated by the time I had conceived according to scan dates so it's obviously a rough guideline.

YANBU
I know when my DD was conceived as we only DTD once that cycle.
She was born 7 months and 30 days later by the calendar but according to my LMP she was 40+8. So yes, confusing.

I do see, soy - just thought it felt like a bit of a pile on, and I could imagine being confused myself!

You aren't stupid. There was a time when none of us knew these things. Many of us got them from books on pregnancy, as well as from our doctors and midwives.

Ignore those sticking the knife in and implying that you are an idiot. It probably says more about them than it does about you.

It was a fair enough question. Those of us with several children have had a fair bit of practice at understanding it now, but there was a time when we were green behind the ears.

To clarify again, I'm fully aware that four weeks isn't a month. But 40 weeks isn't 9 months, as much as 36 weeks isn't.

It's 40 weeks or 9 calendar months + 1 week.

@whiteredrose, unfortuately, your experience is just anecdata too!

My DD was conceived through IUI, so we know exactly when ovulation happened, when sperm was introduced, etc. etc. However, a 7 week scan did not tally with DD's actual gestation, nor did the 12 week scan. That's quite normal.

The important thing is for doctors to be able to use the best data they have. I agree with you that this is bound to change as the technology becomes more sophisticated, but I think it may be quite a slow change.

If you can tell the date of conception, do they still count from previous period?

Technically your pregnancy starts two weeks before ovulation and for most women that is your last period but not always. Until you have a dating scan and official due date, a due date is based on last period.

i had to explain to my mother about the 4 week/month thing and shes in her sixties. She a landlord and was charging her weekly at one point wanting to change it to monthly and i had to explain that she couldn't just times the amount by 4 to get the new amount as she would lose weeks of rent!

I do think that lots of people don't know very (apparently) obviously things like this. Like about 25% of the country think the sun goes round the earth!! its not that they are stupid (necessarily) some people just don't think about this stuff, add maths in and you get a whole new issue :)

There are various complications that might confuse anyone, quite apart from women being in a Schrödinger's pregnancy state for the first two weeks of every month when they are ttc --you both are and are not pregnant as the doctors measure these things for a fortnight out of every month on that basis. (And if you have a twenty-one or a thirty-six day cycle that two week from last period measure is going to be out anyway, because your period is set by the date of ovulation, not the other way round, so you might have ovulated as few as four or five days after your last period or as many as eighteen or twenty.)

A lunar month is slightly more than 28 days; there are thirteen of those in a year, not twelve. And a lot of women, maybe even most women, have 28-day menstrual cycles. So not being sure which of the two sorts of month is being talked about seems quite reasonable to me; there might easily be a connection made between lunar months and menstrual cycle length, and from there to thinking that a lunar month instead of a calendar month might be how pregnancy is measured isn't all that big a step.

Nobody can really know for sure the date that they actually conceived, although in the majority of cases it will be about two weeks after the first day of their last period.

Bollocks. If you only had sex once in the last few months? July 4th in my case.

@Topseyt thank you! Good to know I'm not actually that daft for not understanding this.

@Iamnotacerealkiller - "its not that they are stupid (necessarily) some people just don't think about this stuff, add maths in and you get a whole new issue"

^^ I think this is maybe where I was coming from with the whole four weeks/month thing. I've just never thought about it like that I guess. I also have dyscalculia (like dyslexia but numbers-focused), and so things that are number-related are particularly challenging for me and I don't always draw what seem like the obvious conclusions.

That probably didn't make much sense but I'm basically agreeing with you!

Bollocks. If you only had sex once in the last few months? July 4th in my case.

But you still don't know, right?

Sperm lives for different amounts of time - the difference could be a week or more, depending on the nature of the sperm and of the woman's body. Ovulation and the movement of the egg are likewise not exactly the same for everyone. And even then, fertilised eggs don't all implant at precisely the same time or in the same way.

In my case? About 9 million years! 😂

A calendar month may not be 4 weeks, but a lunar month is, hence why most menstrual cycles are 28 days (4 weeks). So OP wasn't wrong, she just didn't say which type of month!

(Not that it matters, but I don't think most menstrual cycles are 28 days. 28 days is an average, and the majority of people fall either side of it.)