Which is more accurate?

[AFWife]

My u/s due date is Jan 16th and my LMP due date is Jan 21st. I know, not far apart...but which is usually more accurate?

[nova22]

How well do you know your cycle? Fluctuations in your cycle make a big difference when it comes to your EDD. If I use my LMP I know for sure that my EDD will be late because I have a long Phase I and a very short Phase II. In my case, the ultrasound is more accurate unless I can get my HCP to trust me that I know and understand my cycle and can use my chart to determine my EDD.

Case in point: The midwife's little wheel that finds the EDD using the LMP gave me an EDD of December 17. But if I use my chart to determine my EDD, I get December 8. I've had two ultrasounds and two fundal height checks that said my EDD is December 11, which is closer to the date I got from my chart than the date the wheel got from my LMP. Hope that makes sense. I guess I could have more easily answered your question by saying "I dunno" but that didn't seem quite as helpful.

[Nicole730]

I'm not sure...probably u/s I'd think. With both my kids I had a 28 day cycle and ovulated day 14...

DS: LMP April 15, U/S April 17 - born April 16
DD: LMP Feb 28, no U/S - born March 5

[lillymonster]

hmmm...neither, lol! I guess if you had a 28 day cycle, your LMP could be more accurate. This time I did, last pregnancy I did not. Last pregnancy I had like a 32 day cycle, and ovulated on day 18 I think. This time it was 28 days, but I ovulated again on day 16 I think - my LMP date is later then based on my O date.

I was measuring big up until my 20 week ultrasound and was dated ahead, and then now I am on target, so I would go by LMP.

[lyterae]

If you knew that you ovulated on day 14 of your cycle using your LMP would be fine. If I went by LMP my due date would be more than a month off.

[AFWife]

Well, that will teach me to not chart. I have NO idea when I ovulate. I guess I'll just keep telling everyone, "Oh end of January"

[dejagerw]

What ultrasound are you going off of? An early ultrasound or a recent one? I would think an early ultrasound would be the most accurate. A late ultrasound could be off... but so could your LMP date. I probably depends on how regular your cycles are.

[AFWife]

Originally Posted by dejagerw

What ultrasound are you going off of? An early ultrasound or a recent one? I would think an early ultrasound would be the most accurate. A late ultrasound could be off... but so could your LMP date. I probably depends on how regular your cycles are.

Recent. My LMP put me at 17 weeks 4 days and the u/s said 18w2d

[nova22]

Originally Posted by AFWife

Well, that will teach me to not chart. I have NO idea when I ovulate. I guess I'll just keep telling everyone, "Oh end of January"

Probably a good plan...personally, when people ask for my due date, I give them the latest possible date or say "end of December" because I can't stand all the annoying comments at the end of pregnancy. You know...

Haven't you had that baby yet?
When are you going to have that baby?
Are you in labor right now?
You better not have your baby HERE! (as if I maliciously plan for my water to break all over the floor in the checkout line at the grocery store)

and my least favorite of all...

Haven't you popped yet?

Sorry to go off-topic, but yeah, go with the later due date.

[kalamos23]

Unless it's an early u/s (5-9 weeks), I would go with your LMP just so that you have more time. If you or your DH are tall or have long legs, it can throw the results off - DD was measuring 2-3 weeks ahead at 22 weeks, but it was because she was really tall and her femur length was throwing the measurements off. She ended up being 22" long a week early. I was charting so I know my dates were correct. Anyhoo - go with the later date!

[AFWife]

Originally Posted by kalamos23

Unless it's an early u/s (5-9 weeks), I would go with your LMP just so that you have more time. If you or your DH are tall or have long legs, it can throw the results off - DD was measuring 2-3 weeks ahead at 22 weeks, but it was because she was really tall and her femur length was throwing the measurements off. She ended up being 22" long a week early. I was charting so I know my dates were correct. Anyhoo - go with the later date!

DS measured earlier than my LMP and was born at 38 weeks, 7lbs 15oz, 21in

[myk]

generally speaking, the u/s date (if done early) is more accurate. the LMP date doesn't tell you when you actually conceived, it assumes you conceived 14 days into the cycle. my first baby, i conceived on day 7. this baby, i conceived on day 12. the LMP date is therefore off for both.

my first ultrasounds both times were at 7-8 weeks, and the u/s date matched PERFECTLY the ovulation date (which i knew from charting etc). later on (over 15 weeks) it's been off quite a bit because baby's got a big head. the further along this pregnancy goes, the further "off" the dates may be. same thing happened with my first kid, who was born early at 7#11oz, and they said if she went to term she'd be closer to 10 lbs.

[TheDivineMrsM]

Originally Posted by myk

generally speaking, the u/s date (if done early) is more accurate. the LMP date doesn't tell you when you actually conceived, it assumes you conceived 14 days into the cycle. my first baby, i conceived on day 7. this baby, i conceived on day 12. the LMP date is therefore off for both.

Same thing happened with me. I think this baby was conceived on CD9. My original EDD was bumped up 11 days because I was measuring so far ahead at the 12-week ultrasound.

That said... "due dates" are big, whopping guesses anyway. If people ask, give the later date to postpone the inevitable questions from people.

[allisonrose]

With my first, my EDD by ovulation was Sept 27 but by LMP it was Oct 1. I went along with Oct 1 for my hospital midwives because they were OB-like and I would have had to have testing to remain pg past 41 weeks. (I told my family early to mid Oct so my Sept 22 guy was a bit surprising!)

I think generally sticking with the later date is a good thing because of all the pressure to get that baby out!

[MacKinnon]

Well, with my DD my due date was 1/30 by LMP and 2/06 by 20 week ultrasound. She came on 2/10, so 11 days past LMP or 4 days past u/s indicated date. With DS I had no idea, so we did an early ultrasound and he arrived exactly on his due date. This time around I was charting, and I learned that I ovulate late in my cycle, about 5 days later than the 14 day average. I was due 9/8 by LMP, 9/13 by charting and my two early u/s were 9/11 and 9/12. My 20 week was 9/13. I would stick with and plan on the later date, better to err on the side of caution both in terms of risk of induction and in terms of mentally preparing to be later.