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Scans, dates and general confusion!

(22 Posts)
astormgivenflesh Sun 30-Oct-16 09:57:29

Ok so I might just be being a complete fool but I cannot for the life of me work this out

Original due date, based on LMP was May 17th 2017

Had scan where sonographer said I was earlier than I thought, put me back to 9 weeks 6 days and updated due date to May 27th 2017

Talking to midwife, she said I must have conceived between Aug 28th and Sep 3rd but an app I use says I conceived on the 20th Aug.

I had a progesterone test on the 30th Aug which was too low to have ovulated in the week previously and a second test on Sep 9th which was high suggesting ov around Sep 2nd which would fit with conception estimations of the 28th - 3rd but this wouldn't allow the baby to be 10 weeks at this point so how can it be possible?

I'm just very confused! Please someone make sense of it all!! cakeflowers

MoonlightMojitos Sun 30-Oct-16 10:47:06

2 weeks is added to ovulation date/actual gestational age so make your 'pregnant' date. So if you ovd 2nd September then on that date you would have been '2 weeks pregnant', making you 10+2 today. Does that make sense? It's silly the way they date it I know.

MoonlightMojitos Sun 30-Oct-16 10:48:23

Oh so yes the midwife is correct, the app is wrong (which you knew as the progesterone test showed you didn't ov yet)

astormgivenflesh Sun 30-Oct-16 13:08:18

Thanks for your response! It's the timings I'm confused about though - if I conceived/ovulated on 2nd Sep say, which would completely make sense progesterone test wise, HOW can the baby be ten weeks?

MoonlightMojitos Sun 30-Oct-16 15:31:31

It's not, the baby is 8 weeks but you are 10 weeks pregnant. Because that is just how it is dated.... you were "2 weeks pregnant" on the day you ovulated. It's how they date it going by last period.

MoonlightMojitos Sun 30-Oct-16 15:36:22

This might help?

astormgivenflesh Sun 30-Oct-16 15:53:05

You are so helpful, thank you! Thing is, my period was Aug 10th so I can't be 8+2 going by last LMP.
I'm sorry if I'm being super dense, I really appreciate your help xx

haveacupoftea Sun 30-Oct-16 16:23:02

But you aren't 8+2, youre 10 weeks. Its been 8 weeks since the sperm met the egg so that makes you ten weeks pregnant. You just ovulated later in your cycle so you arent as far along as you originally thought.

MoonlightMojitos Sun 30-Oct-16 17:45:07

I don't know how else to explain it sorry, what ever date you ovulated you add 2 weeks to that to get how many weeks pregnant you are!

astormgivenflesh Sun 30-Oct-16 18:03:45

I add two weeks to the date I ovulated? So two weeks to 2nd Sep is 16th Sep. How does that work? xxx

voxnihili Sun 30-Oct-16 18:17:18

As far as I'm aware you count from your period, which would be about 10 weeks. A lot of people don't know exactly when they ovulated. For example, I don't track ovulation. If I conceive this cycle, I'll likely find out next weekend when AF is due. By then, it will be 5 weeks since my last period so I'd be 5 weeks pregnant. It would only have been 2 or 3 weeks since ovulation but there's no real way of knowing when ovulation happened, but we all know when our last period was so I think that's why they use periods rather than ovulation.

The weeks are approximately 2-3 weeks prior to ovulation depending on your cycle.

confusedat23 Sun 30-Oct-16 18:53:15

Ok so... You are thinking when moonlight says add 2 weeks on its the 16th sep?... Well then take two weekd off your ovulation date and that gives your pregnancy date?

astormgivenflesh Sun 30-Oct-16 18:57:53

If I count from my period, I'm over 12 weeks.

Scan has said this is incorrect and I'm actually 10 weeks - my confusion is bc I had two progesterone blood tests in between my LMP and finding out I was pregnant

If I ovulated on the 2nd September which seems likely given progesterone results, baby wouldn't be 10 weeks though! Ppl then suggested adding or taking away weeks so I'm absolutely confused now!

SolomanDaisy Sun 30-Oct-16 19:04:18

If you ovulated on 2nd September, your pregnancy is dated from 19th August which is two weeks before ovulation. This makes you just over ten weeks. The midwife is right.

confusedat23 Sun 30-Oct-16 19:05:59

Ok so doctors start your little babies life 2 weeks before ovulation... Therefore your baby is already 2 weeks old on the day you ovulate.

astormgivenflesh Sun 30-Oct-16 19:07:03

So that would put conception at around the 2nd Sep and EDD at May 27th, despite my LMP being 10th Aug??

Thank you all so much for responding, I'm sure I'm being absolutely ridiculously dense cakeflowers

willitbe Sun 30-Oct-16 19:11:31

I have written the dates down for you, hope it makes it clearer!

According to scan:
10th August 2015 LMP (real)
20th August 2016 LMP (equivalent as you ovulated 10days later than normal)
27th August to 3rd September Fertile period (could have intercourse at any time in this period in order to conceive on the:
3rd September 2016 Conception/ovulation date
27th May 2017 due date

So pregnancy dates equivalently:
So 20th August 0 weeks
30th August 1 week 'pregnant' - eg pre-ovulation (ties in with blood test)
3rd Sept 2 weeks pregnant (ovulation date, conception occurs within 24 hours as that is how long the egg lasts.)
9th Sept (6 days post ov - high progesterone confirming ovulation a week before, this test can account for anywhere 6 to 9 days post ov, usual to guess it is 7days post ov, hence the estimated 2nd Sept date given)
17th Sept 4 weeks pregnant (possible to have positive pregnancy test by now)
28th October 9weeks 6 days pregnant (I assume this was when the scan was done?)
27th May 40 weeks- due date

Remembering that early scans can be out by 3 days either way, and that ovulation tests can be out by 3 days, the above dates are given working on the scan being the most accurate and matching with the ovulation tests.

The important thing to remember is that the due date is just an estimate too, it is +or- two weeks, eg 38 to 42 weeks are considered all normal range for birth!!!!!!

The most accurate dating time for scans are between 12 and 14 weeks, so if you have another scan in the next couple of weeks, they may measure differently by a couple of days again.

Congratulations on your pregnancy!

astormgivenflesh Sun 30-Oct-16 19:18:57

Willitbe you are so very wonderful, thank you so much for making it so clear and easy! I get it now, thank you!

Pregnancy is very confusing with all the odd dates etc but this was brilliant! cakeflowersflowersstar

GiddyOnZackHunt Sun 30-Oct-16 19:38:11

Do you have regular 28 day cycles?If I'm reading your posts right it doesn't sound like you do. In which case LMP can be misleading. In a 28 day cycle, ovulation usually occurs at day 14 and therefore you are treated as 2 weeks pregnant on the date of conception. In most women that coincides roughly with the start of their last period and is a firm date a woman should be aware of.
If you have say 36 day cycles or irregular cycles, this all falls down and you need to figure it out in other ways.

astormgivenflesh Sun 30-Oct-16 19:59:01

No, my periods are really irregular; anything from 28 - 45 days!

GiddyOnZackHunt Sun 30-Oct-16 20:13:16

That explains your struggle to fit your pg into the standard model then! In your case you date your pg by scan or if you know when you ovulated, from 14 days before that. Congratulations BTW smile

ShowOfHands Sun 30-Oct-16 21:15:42

The way for it to make sense is to think about it in terms of what we once would have known about pregnancy. Before we had scans and progesterone tests and fertility trackers.

It was noted that pregnancy seemed to last for around 40 weeks from the time of a woman's last period so that made sense as a way of dating. Of course we later found out that for an average woman, actually ovulation and conception takes place 2 weeks after the last period and therefore you're technically pregnant for 38 weeks. However, accurate scans are very modern and we're creatures of habit and we're used to the 40 weeks thing so your estimated due date remains 38 weeks from conception but we still count from 14 days before then and call it 40 weeks.

A textbook woman will have a period and then 14 days later ovulate and conceive and 14 days later will have a missed period and then 36 weeks later have a baby. We call that woman 2 weeks pregnant on the day of conception, 4 weeks pregnant when she misses her first period and give her a due date 40 weeks from her last period. 40 weeks which includes 2 weeks at the beginning when her body flushed out the last egg and uterine lining and made a new lining and matured a new egg.

You're not average though. You ovulated later than 14 days into your cycle which is part of the confusion.

Given an average pregnancy, you will give birth somewhere between 37 and 42 weeks after your last period. The estimated due date is just a number to help plan care and only a rough approximation of when you'll give birth. As a first timer, it's more likely your baby will arrive early June tbh!

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