Which dates did you go by for EDD? 12 week Dating scan or Cycle?

[lilimama]

I know that I was exactly 12 weeks on the day of dating scan. That is, according to first day of last MP. But the scan came up with 12+5. I know that the policy is to go with the dating scan, but why is that when all the scan does is measure the length of the spine? Surely the ovulation/conceptions dates etc are more accurate? Both my doula and my midwife are on vacation during the dating scan estimated due date but not during the earlier estimated due date according to my cycle. Whatever it is, it doesn't matter I'll find another doula and midwife but I'd just like some opinions/experience so I know what I should expect.

Thanks!

With my other two it was by the dating scan. Though second time round I thought it was 3 days out. I was right (though it could just be luck). This time round the dating scan was a whole week out from what I thought. Have since had numerous scan and the last couple both agree with the date I have. We shall see! The dating scans are based on the average baby though so only a best guess.

i would go by whichever was later! lol that way it gives you a bit of leeway if you go over and they start pushing for induction.

if you know your cycle really well, and how long it is then go with your cycle dates.
midwives will usually date it based on a 28 day cycle though, which you may not have

It's because people have varying cycles length and different luteal phase lengths so going by the LMP isn't always accurate. But scan dates aren't always accurate either

I went by my ovulation date and the scan date was five days out too. THe midwife etc wanted to go with the scan day even though I knew the scan date was wrong. It would have to have been an immaculate conception!!

I go by scan. Unless you know the date of conception!

your period may well have been 12 weeks ago but you may have ovulated earlier/later in that cycle, i had an early scan and it dated to about a day or two either side ov my ovulation date so it was pretty much exact. when i went back at 12 weeks the scan was 4 days different from the first scan putting my edd at a later date. i wouldnt worry too much a difference of 5 days is nothing to worry about xxxxxxxx

I thought policy was that you go by LMP unless there is a difference of more than 5 days in which case they would use the scan.

In practice I think they always use the scan.

Both methods are only an estimate anyway.

FWIW I knew the date of conception of DTDs. There was only 1 possible date. I was over-ruled by about 4 days with a scan. When they were born at 26+6wks (by scan) I was told they were more likely to be closer to 27 1/2 weeks...as days make a huge difference for a prem baby. I was right after all (funny that)

and the scan doesnt just measure the length of the spine they take several measurements from the baby including crl, femur length and so on. babys before 13 weeks all grow at pretty much the same rate give or take a day or two so a scan at 12+5 would be pretty accurate but have an error margin of about +/-3-5 days either way x

I go by the scan date. There's so much more involved in conception beyond the date that you and your DP had sex - actual ovulation date, fertilization, implantation - unless you know all of those factors, just easiest to go by scan dates. LO will come when it comes anyway...!

If I had gone by LMP my due date would have been and gone by now! I'm not due for another 6 weeks - (I rarely have AF's btw due to PCOS)

TBH I didn't know that anybody went by LMP anymore, except as a guide until the scan.

I would order it in terms of reliability:
Date of conception
Scan
LMP

DP was away! I know when I conceived pretty much so it would have been an alien visitation and the only reason I'm bothered is coz I was hoping to go for the only midwife in town who will support my HBAC! So it does feel pretty important to me. Coz of scan dates being diff I would have to go through hospital system which is a very different experience IMO. I can also opt to leave the country for a few months and come back to UK. Thanks for your imput! x

conception can occur 5 days before, on the day of and 1 day after ovulation, this is because sperms can live for up to 5 days until the egg is released and the egg lasts for around 24 hrs after it is released. so you cant base conception on the day tou had sex i concieved 2 days after i had sex because this is when i ovulated and the scan pretty much tied in with that too. Its quite confusing trying to work out exactly when you concieved if your absolutely sure of when you ovulated then go by your own dates afterall you know your body best, however if you are basing it on the day you had sex id go by the scan xx

sorry conception occurs on the day of ovulation bu u know what i mean xxx

Lilimama - it's only 5 days difference, and you really can't predict when the LO will make an appearance. If your mw is away on one date and not the other, there's no guarantee that it will come before she goes away.