Has the method of calculating changed?

[endofthelinefinally]

Recently I have seen discussions when posters say they are 3, 4 weeks pregnant. I am a retired midwife and admittedly probably out of date. However, EDD was always calculated from the first day of LMP. So generally 5 weeks would be the earliest one would get a positive test.
Can anyone explain this 3/ 4 weeks pregnant thing and is this universal now?
Thanks.

It's because one brand of pregnancy test does it that way.

And also because some people test at or before the day their period is due.

I tested before my period was due

I found out 2 days before my missed period and I was 3w+5 days. Tests are really sensitive these days!

Because they are wrong, simple as that

Does that not cause confusion with dates? Presumably the midwife will estimate the due date in the conventional way and the pregnant woman will readjust the dates? Otherwise I can imagine some confusing conversations in the antenatal clinic, given that blood tests, scans etc are based on conventional calculating.

Retired doc here. Yes, OP, I’ve noticed these strange timings on here too! I don’t think our colleagues have changed anything, it’s just ignorance on the part of patients. I’ve had to explain to some who were puzzled why term pregnancy is described as being 40 weeks, when that would be “ten months”!
I assume the posters are counting from the theoretical date of their missed period, not the actual known date of their LMP.

I can imagine a situation with bleeding in early pregnancy where woman and hcp could be at cross purposes.
Oh well. I suppose it isn't my problem any more. I was just puzzled.

I was 3weeks 4 days when I found and that’s using the conventional dating system from LMP- I started having morning sickness several days before my period was due so took a first response test.

Maybe at home tests are more sensitive?

I did get a positive test before period due, I count that as too early to say I'm pregnant as I've had too many chemical pregnancies. I count from 2wk late so 6wk pregnant onwards, many have been unsuccessful after that too. So far so good with current one, 9+5 by lmp atm.

@endofthelinefinally

Does that not cause confusion with dates? Presumably the midwife will estimate the due date in the conventional way and the pregnant woman will readjust the dates? Otherwise I can imagine some confusing conversations in the antenatal clinic, given that blood tests, scans etc are based on conventional calculating.

Yes, but the confused person is the newly pregnant one when it is her first pregnancy and she encounters maternity services and chat groups for the first time.

Any confusion doesn't last long

@endofthelinefinally

Does that not cause confusion with dates? Presumably the midwife will estimate the due date in the conventional way and the pregnant woman will readjust the dates? Otherwise I can imagine some confusing conversations in the antenatal clinic, given that blood tests, scans etc are based on conventional calculating.

Yes midwives still go by lmp until the dating scan gives the official due date.

I notice the earlier dates too which doesn't make sense (I'm not a medical professional).

I've always assumed it's people testing early, from before their missed period or they rely on the number of weeks on the Clear Blue digital tests, which very clearly notes its weeks from conception rather than from you LMP.

I was 3 weeks 1 day from LMP when I found out, by my now adjusted dates from my dating scan I was exactly 4 weeks pregnant on that date so 5 weeks definitely isn't the earliest

What is the conventional way to date?

I was pretty certain of my conception date (give or take 2 days) with dc2 - we dtd once that month, and I get ovulation pain so it was easy to narrow down conception to a small window. I still used LMP as my official date for counting the pregnancy as that's what the MW will use.

The only real dates that matter in medical terms is LMP and whatever date is them confirmed at the scan.

Home tests definitely give you a positive way before 5 weeks these days. Not sure why you and several others are assuming women are wrong. Plenty of people who are actively ttc test before their missed period so would know when they are between 3 and 4 weeks - that usually is going off LMP.

Working back my positive test was at 3w4days.

@SatsumasOrClementines

What is the conventional way to date?

The pregnancy is initially measured in weeks from the first day of your last period. All scans/booking in etc is calculated off this.

At the dating scan (usually around the 12 week mark), the due date is estimated and the pregnancy is "dated" in weeks and days. This usually includes the two weeks between first day of period and conception, as these don't last the same length of time for everyone.

I have a friend who told me she is 2 weeks pregnant. She won't be told otherwise

@endofthelinefinally @Babdoc In the main I don't think it's pregnant women getting it wrong - it's because you can buy tests that are very sensitive, and from Amazon you can buy them cheaply in bulk so more people are testing early (before their period is due). If you're using a £9 branded test you might be more likely to wait until after your missed period. If you're using one from a pack of 20 that cost 50p each you're less likely to worry if you waste one because it's too early. I got my 1st positive at 3+5, before my period was due. It was a real squinter at that point but still a line. This does come with its own problems of course - you see so many messages about lines that come and go or are barely visible at all and more and more chemical pregnancies being detected.

There are a few people who get confused by the digital tests as well. Those give you a written message that says "3+ weeks" when you're actually 5 weeks from LMP (although obviously imprecise as based on HCG levels which vary). This seems to be a minority though and someone quickly points out the mistake if they post on here.

It’s because some of the modern tests will pick up pregnancy very early, before your period is due. So people test (for example) 3 weeks and 4 days after the first day of their last period and get a positive result despite only being 11 or so days after ovulation.

Thanks @BernadetteRostankowskiWolowitz

Is dating scan due date based on when you conceived? IVF for example would surely give you a very good idea of a due date.

I always thought you were typically 4 weeks once your period was due? A 28 day cycle is 4 weeks. I starting getting positives a week before my period was due so I was technically 3 weeks when I found out.

@SatsumasOrClementines

Thanks *@BernadetteRostankowskiWolowitz*

Is dating scan due date based on when you conceived? IVF for example would surely give you a very good idea of a due date.

I'm pretty sure they date at the scan based on measurements so average measurements for each day of pregnancy. These will have all been assigned based on the typical "two weeks beyond conception" so an IVF pregnancy will be two weeks longer than actual (at 12 weeks if they say an IVF baby is 12w4d then conception would have likely happened at 10w4d, same as with a non IVF pregnancy).

Does it cause confusion?
No really.

Poas. Stick says pregnant. Do online calculator from LMP which says 3 weeks 5 days.

Book early scan at around 7 weeks. They say 7 days 1 week. If questioned explained that you don't necessarily get pregnant the day you concieve.
Book in for NHS scan at what should be 12 weeks. Told you're 12+2. If questioned explain its v difficult very early to get accurate measurement as it's only a mm here or there but this is what we'll be going from.
Give birth some time in the vicinity of "40" weeks

I always had long cycles with ovulation at about the 25 day mark. If I took a positive test and told the dr the date of my lmp they would tell me I could be 6/7 weeks pregnant. When in fact I knew my ovulation was approximately 11/12 days prior to me having a positive test. So in fact I was just at the 4 weeks pregnant mark 'physically'