The weird way we date pregnancies

[YireosDodeAver]

A chat thread entirely unrelated to a recent thread that got a bit hot and bothered and had to go and have a quiet lie down.

@honeylulu You particularly mentioned how silly it is, the way we date pregnancies from 2 weeks before we get pregnant.

I wrote a reply and couldn't post it, but we can use this thread to rant further about how silly it is....

My view - yes it is a stupid method but changing it would cause deaths so be a bad idea.

The knowledge that conception happens about 2 weeks after last menstrual period is relatively recent knowledge.

Midwives and obstetricians have been working with knowledge of women's bodies developed and passed down from expert to pupil for thousands of years during which the only reliable data point was date of last period.

All that knowledge is based on dating pregnancies from that start point. all the rules and thresholds are based on that system.

If the whole of midwifery and obstetrics suddenly decided overnight to date from ovulation day instead, mistakes would definitely and certainly be made with confusion about what was meant when a rule said a level is dangerous at 10 weeks - is that old weeks or new weeks?

Babies would die in the confusion

It is not worth it just to save us the headshake moment when you realise you count as 2 weeks pg the day you conceive, and in weeks 0-2 you were not actually pg.

I was pregnant 9 days before I had sex after I had my iud out. Therefore my daughter must be Jesus!

They do actually revise due dates sometimes if the development of the embroyo doesn’t match up with the last menstrual period. It’s more likely to happen to women with longer than average or shorter than average cycles. Sometimes women with very erratic cycles (so perhaps not having 10-13 periods a year but fewer and at unpredictable intervals) will be offered an early dating scan. I’m pretty sure drs also have a dual system of dates with different names - weeks gestation vs weeks pregnant or something. That might be true in the UK though…

I guess maybe as well as tradition and problems that might occur form changing the system it’s helpful to have official definitions that don’t rely on scans for legal reasons. Legally you don’t have to agree to scans but there still needs to be a due date for things like calculating maternity leave.

Good point!

I was pregnant 11 days before my LO was conceived via ivf in another city! (I wasn’t even there when the magic happened!). Honestly blows my mind!

We don’t use just LMP to estimate ( the clue is in the name) date of delivery, we use accurate dating scans.

@Jojobees that's not the point. With all the dating scan and other corrections, you still work backwards to Day0 being 2 weeks before you met the father of the child if it's a one-night-stand situation.

Hello @YireosDodeAver
Thanks for starting this thread so I can rant a bit more!
I do get what you say about the risks that could be run if the historic method was suddenly changed. But it still annoys me anyway!

The OP on the other thread was (presumably) a woman and didn't seem aware of the "fake two weeks" added in to the beginning. I wonder how many awkward situations have occurred with men thinking hang on I can't be the dad because six weeks ago I was still abroad so if she has been pregnant for six weeks.....

When i conceived my youngest I was having 50 day cycles. I knew exactly when i conceived because I was doing ovulation tests but I kept being told I was "10 weeks pregnant" when I knew I was only 6 weeks (or 4 in real terms). It drove me crackers. Luckily the consultant adjusted it on my records after the second scan or I would have ended up being "pregnant " for 10 months!

Day 0 of an estimated 280, anything from 259 to 294 are normal. But that’s 280 days from the 1st day of your last menstual cycle, not actual pregnancy. Conception can never be day absolute 0 as everyone’s bodies work slightly differently. We have to use something. This works.

I could rant for hours about how much this has confused me during this pregnancy!

the cycle I got pregnant my LMP was the 1st - 5th of the month, therefore you’d think I’d ovulate around 15/16th, in a 31 day cycle. But nope, baby measured small early on so they pushed my due date back and apparently I would have ovulated around day 23🤷‍♀️

what’s even more confusing is that I had a scan at the epu and measured 7 weeks, the dr told me I would have conceived 7 weeks prior, not 5 like you’d think🤔

@Jojobees it works fine for many purposes.

An example of when it doesn't work

Scene one - no dialogue. In sequence of montage we see a man and woman on holiday meeting for the first time, clearly attracted to one another, and having sex, spending the rest of the holiday together and returning to England arm in arm, a new relationship formed.

Scene two - a flat in England
She - Darling I need to tell you something. We've only been together a few weeks but I love you, and I have just found out I am pregnant
He - oh my god. Wow. Of course I will do the right thing but I have to ask, is it definitely mine?
She - yes there has been no one else, only you.

Scene three
ObGyn - so welcome to your dating scan. Just checking your last menstrual period was?
She - well it was about a week and a half before I went on holiday so um about 4th July
ObGyn - ok let's put some gel on your tummy and do some measurements. Yes there's the backbone and there's the heartbeat and let me just measure here. Ok so by LMP you are at about 11weeks 5 days and yes you are measuring at 12 weeks so baby is growing beautifully congratulations
He - 12 weeks! You swore there had been no one else but we only met 10 weeks ago. You tricked me. I am out of here. (He leaves)

What pisses me off is not the stupid way we date pregnancies from day 1 of your period, 2 weeks before you have sex. That I can live with.

It's the fact that when you get your earliest possible pregnancy test, around the end of your normal menstrual cycle, you're told you're FOUR weeks pregnant. And 2 weeks after your missed period is stated as SIX weeks pregnant.

Which is absolute nonsense. In reality, six weeks is more like two weeks pregnant.

All the nasty anti woman, anti choice nut cases base their hatred on this, thinking women have a whole six weeks to decide whether to keep on a pregnancy when the reality is just around two weeks.

I was in the middle of replying, deleted, and said to myself, 'OldTinHat, I don't even think that head gear will protect you if you post anything right now...'

Ok, but if he’s sim enough not to understand the way pregnancies are dated did you really want him to stick around? It’s a simple explanation. One I give 30/40 times a week.

Because i did IVF i knew the exact date of conception but the midwife insisted i was overdue when i knew I had another week to go. She deliberately broke my waters during a sweep to hurry things along, which resulted in an infection, unwanted induction and the typical associated cascade of intervention, and both i and my baby nearly died.