AIBU to be thoroughly confused about pregnancy calculations? :D

(13 Posts)
whyistherumgone Fri 11-Nov-16 13:32:21

Posting here for traffic but also feel like I'm one of the only people who doesn't 'get' how this is worked out.
Be gentle with me, I'm new to all this grin

So my period was late, took a test - positive. Worked out that I would be around 2 weeks now according to conception/ovulation.
Took a CB digital to be sure - it said 1-2 weeks.

Looked online 'what to expect at 2 weeks' etc as I was interested - it says 'at 2 weeks you're actually considered to be 1 month pregnant because of the way it's calculated'.

Thoroughly confused! I'm sure the doctor will explain all this to me next week but I'm keen to know everything ;)

GailLondon Fri 11-Nov-16 13:35:56

The standard way to count pregnancy is since the first day of your last period. So you are considered ~4 weeks pregnant even if conception was only 2 weeks ago.
Yes its silly, but that is the standard method of counting that all doctors and midwives will use so you should just use it too!

whyistherumgone Fri 11-Nov-16 13:39:53

Thank you - so just to be clear -do you have your 12 week scan when you are actually 12 weeks, or do you go by this standard method?
Just working out when the 'safety zone' would likely be if we get that far (fingers crossed).

peppatax Fri 11-Nov-16 13:43:05

Point of conception is irrelevant, it's always dated from earliest point of possible pregnancy i.e. first day of last period as that's a standard measure across the board. Your due date will just be a midpoint of essentially a month long period of when the baby could deliver depending on the actual date of conception (which could have been a few days after your period, or up to 4 weeks after). It's just a guideline. Count 12 weeks from date of last period and you should be fine.

LeeFiora Fri 11-Nov-16 13:43:08

12 weeks from last menstrual period, so 10 weeks after actual conception.

Congratulations smile

peppatax Fri 11-Nov-16 13:45:03

Sorry I should add, they may change the estimated date based on size of the baby at 12 weeks but again, this is just a best estimate based on historical size data and may not be relevant to your actual delivery date as so many other factors other than baby size to take into account!

whyistherumgone Fri 11-Nov-16 14:01:15

Thank you smile
Sorry, it's probably a really stupid question! So much to get my head around, all being well smile

GailLondon Fri 11-Nov-16 14:03:47

Good luck with your pregnancy! So its good news really,, you don't have as long to wait untill you reach 12 weeks as you are 4 weeks already!

peppatax Fri 11-Nov-16 14:27:55

There's so much to learn! Enjoy and get info from MN as much as possible!

MissDuke Fri 11-Nov-16 14:32:54

Yes it is dated from first day of the last period because this is a date that can be easily pinned down. The date of conception is tricky - most don't know the exact time of ovulation and even then - there is a few days when conception actually happened and implantation is even later. So it is easier to use the start of the cycle as the date. So forget about when you think you conceived and just go by the weeks from your last period from now on. Believe me, everything about pregnancy is bewildering, this may as well be too grin

Congratulations flowers

baconandeggies Fri 11-Nov-16 14:43:27

EDD calculators work on the assumption that a woman has a 28 day cycle with ovulation on day 14. A woman's 'estimated due date' is then given as 38 weeks from ovulation..

So a mum being '4 weeks pregnant' means the egg was released from the ovary approx 2 weeks previously. Think of the 1st day of your last period as when it all began for your baby... So yes - the '12 week scan' is approx 10 weeks since you ovulated.

There's a lot of individual variation though - most accurate is if you know for sure when you released an egg, as it can only live for 24 hours or so. Though you might release from the other side the next day...

Dating pregnancy from when you had sex is less accurate, as sperm can survive in the fallopian tubes for many days.

And then there's the fact that women usually give birth on average any time from 37 - 42 weeks anyway!

Congratulations smile

CesareBorgiasUnicornMask Fri 11-Nov-16 16:08:32

Congratulations 🎊. They'll date accurately at your first scan. But assuming you have regular cycles the first day of your lmp is thr best guide.

I'm really confused currently as got a BFP today grin but my lmp was at the beginning of September and I've been feeling pregnant but testing negative for aaages. Last negative test was Tuesday. And my cycles are spectacularly irregular. And I can't actually remember when DH and I last dtd but it's been a while as we generally have a toddler starfishing in the bed between us. So it's going to be a voyage of discovery when I go for the scan!

whyistherumgone Sat 12-Nov-16 10:50:57

Thank you, think I've got my head around it now!
So strange still as I don't feel pregnant at all - barely any symptoms.

Wow Cesare congrats - that does sound v v confusing though!

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