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Due dates. LMP or Scan?

(20 Posts)
justlookatthatbooty Wed 29-Jul-09 07:22:27

So does anyone consider their LMP dates to be more accurate than their scan due dates? What makes the scan dates so "accurate" i.e accurate enough to be the system with which the dr's and midwives calculate when the baby is due and schedule inductions and sections around that date? Genuinely curious.... when our mother's didn't have any scans LMP was the only way to go right?

My LMP shows that I'm 39+3 today which seems very different from 40+3 in the medical profession's eyes. I'm coming under pressure for interventions as I'm trying for a VBAC but I remain convinced that things are just fine, I don't feel like I'm "over-baking" DD and this leads me to be very curious about the estimation of Due Dates. Esp as conception was not physically possible earlier (as per due dates given by scan) as DH was away!

Anyone else a week out on the two different systems of calculation?

ohmeohmy Wed 29-Jul-09 07:30:16

I am no expert but think they are all fairly arbitrary. Different countries use different methods. All women are different so why would we all gestate for exactly the same amount of time? Similarly we are all different sizes so why would a baby from very tall parents have the same size bones (which is what they measure in the scan) as a baby from short parents? Normal is considered to be 37-42 weeks.

Trust your instincts and ignore the fearmongers. If there are no indications of anything amiss and they are pressuring you on issue of dates/scan dates alone then just say you will wait.

l39 Wed 29-Jul-09 08:03:01

I have exactly a week difference between LMP and the dating scan too. My midwife was puzzled as to what to go by, saying that less than 7 days difference she'd leave it as the LMP and more than 7 she'd change it to the scan. At my last checkup she phoned the hospital to ask what to do about a 7-day difference and they decided to leave my due date at that indicated by the LMP, to my relief as I hope for a VBAC too! So I'm 29 weeks tomorrow, not 30.

Can you get to the hospital for frequent scans? Would they agree to leave you longer and scan you every other day? One of my sisters went every other day for 2 weeks for checks because she wanted a home birth and that wouldn't be possible if she was induced. She'd been booked late in pregnancy so no dating scan - the baby was finally born (at home) 4 weeks after the due date (though I'm sure that date was wrong, they'd been urging her to be induced for a fortnight).

justlookatthatbooty Wed 29-Jul-09 08:52:32

Thanks for your responses and assurances.

Very interesting l39 that your midwife checked with hospital and they said to go with your LMP. My midwife was adamant that we were obliged to go with the scan dates even though I couldn't have conceived according to their dates.Also interesting re your sister....did she have a scan every other day to determine size/growth? or just to check all was ok? And good for her that she sat it out 4 weeks after due date, even if dates were wrong. It's so easy to become EDD obsessed. So I feel like I'm 39+3 and I'm going to go and facebook it to stop everyone from phoning and messaging every day. So irritating!!!!!

l39 Wed 29-Jul-09 10:01:07

I think the scans were to check the blood flow in the umbilical cord. My niece had red peeling skin when finally born but was (and is) in good health.
Good luck with the birth!

mafog Wed 29-Jul-09 13:51:22

My DH has had a lot of dealings with Midwives (professionally wink ) and says that many hospitals often bring the due date forward by 2-3 days when scanning so that they can start talking about inducement at 10 days over rather than 14 days. This has been the case for me in all 3 pregnancies.

After I went over with my first and the actual birth was nearer my LMP fate rather than my scan I fixated my due date as the latter one in each case, and that's what I told people, saves a lot of phonecalls.

I also know I ovulated on day 16 of my cycle than day 14 so it stands to reason it would be a bit later.

Loopymumsy Wed 29-Jul-09 19:52:15

Message withdrawn

mrswill Wed 29-Jul-09 20:05:35

I was exactly the same as you OP having my dd this time last year, i knew exactly when last period was, when i ovulated, b'd etc (obsessed emoticon). So i was shocked when they said i was a week further on than what i knew i was. Wish id stuck to my guns, as ended up having the usual induction c section story, which just confirmed to me my own personal dates were right. Stick to your guns, especially if your after a successful VBAC. Best of luck!

justlookatthatbooty Wed 29-Jul-09 20:36:22

Really helpful posts, thankyou. I'm going to stick to my LMP dates!

wasabipeanut Wed 29-Jul-09 20:41:44

I asked my midwife about this as I have consistently measured 6 days ahead on scans and she said if its less than a week they stick to LMP.

Suits me as I'll be trying for a VBAC too. Best of luck with yours!

madmissy Wed 29-Jul-09 20:44:44

same here with the week buffer thing

Mole007 Thu 30-Jul-09 14:28:33

Have to admit that I am going with the scan date. My LMP date is later, but they just did not take into account the fact that my cycle was shorter than 28 days and I seemed to ovulate very early in the cycle, so the scan dates actually fit better! Having said that, if they do start talking induction too soon, then I may well just change my mind grin

mears Thu 30-Jul-09 14:32:40

As a midwife I go by LMP if the woman is sure of when that was. Nowadays though, I am surprised by the number of women who do not know the date of their LMP.

Deemented Thu 30-Jul-09 15:28:26

Going from my LMP i am due on the 13th January. The 'dating' scan put it at 19th January, so there's almost a weeks difference.

I am positive that LMP was 8th April as i've only had 3 periods since dd was born. Am seeinf my MW tomorrow so will ask her about it then.

LittleMonkeysMummy Fri 31-Jul-09 08:12:37

According to my LMP my due date's the 8th of December but according to my scan it's the 30th of December hmm- over 3 weeks discrepency. HAving said that there was a 2 week diference with DD.

I've never had regular periods so I'm more inclined to go with the scan date but that's maybe just me grin

2littlemonkeys Fri 31-Jul-09 09:46:27

Going from my lmp i am due on the 5th november but according to my scan they are saying 12th december. They are going with the scan date which i am very angryabout as dd1 was 15 days late and was 8,11 and my dd2 was 9,1 so i have big babies. I really dont want to give birth to another turkey lol and they are already saying this one is larger for my dates!!!

So why cant they just go with my date argh!!!!! xx

2littlemonkeys Fri 31-Jul-09 09:51:42

LOL pregancy brain striks yet again!!! LMP date 5th nov dateing scan 12th nov xx

sobloodystupid Fri 31-Jul-09 10:00:21

If i went by my LMP ds would've been expected on 31 December 2008, going by scans he was due on 3 February and arrived (finally) by induction a week later!. I have irregular periods so obviously ovulated many weeks later than LMP would suggest. congratulations!

Deemented Fri 31-Jul-09 10:32:19

Gah!!! MW has just been and it seems that the scanning told me the wrong details - I'm due on 19th Jan according to them, which makes me 15wks and 2 days, not 15wks 4 days as i thought!!

mears Sat 01-Aug-09 13:55:46

Deemented - if your LMP was 8th April, your EDD by dates would be 15th January (you add 7 days and 9 months).

Since your scan says 19th, I would go with your own date.

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