Source
r/BabyBumps•
thevariablecause

For those who relied on ultrasound dating rather than LMP, how accurate was your EDD?

FTM here, and I had stupid cycles pre-pregnancy so we relied on a dating scan rather than my LMP. I read somewhere that the whole “baby can come two weeks earlier or two weeks later” line that people keep saying is usually the result of bad math with the LMP, and that with dating scans it’s a lot more accurate. So for those who relied on the ultrasound rather than their LMP—is this really a thing? Did baby come very close to, if not exactly on, your EDD?

Edit to add: I’m at 31+2 and not super obsessing about my due date, btw. I’m just really curious/fascinated by the numbers and the technology, and whether or not there’s an actual accurate way to do “pregnancy math,” if that makes sense. I like to look at numbers for mindless fun—not to draw conclusions, but to see if there are any fun or interesting trends.

Posted Sep 27, 2018, 9:30 AM UTC · edited

1349
hersheykiss7761Mom of 3!•

My first and second were based on ultrasound, third based on LMP. First, scheduled CS at 40 weeks. Second came naturally at 41+6. Third came at 39+1. I heard it also has to do with your body/how long it takes you to "cook" a baby. Just like in one persons oven you can cook a dish in 30 minutes and in another oven it may need 40 minutes.

13
thevariablecauseOP•

That makes sense. I mean I’m sure there are general trends to all these things but it really isn’t an exact science at the end of the day.

2
itsmeeloise87Boy born 7/22/16, #2 Due May 3 2019•

With my son, we went off ultrasound because I ovulated late (didn't even get a positive pregnancy test till CD 35). I truly believe this was far more accurate than my LMP due date- they were nearly two weeks off. His measurements during pregnancy lined up with the ultrasound dating as well. He ended up being born on the early side, 37+6, so much closer to the LMP due date, but he was definitely early because he was tinier than he might've been had he been born closer to due date.

This time around, my LMP and ultrasound dates were far closer- LMP due date was May 1, ultrasound said May 3. I did ovulate a bit on the later side, but not as extreme as with my son.

8
Helloblablabla•

Same! Mine was closer to LMP date than ultrasound date, but ultrasound date was definitely more accurate. She was little too, and very sleepy at first. She was born at either 37+6 or 38 weeks (doctor gave me 2 days for due date as she measured exactly between)

1
derpachoo-magu•

...usually the result of bad math with the LMP...

That's not true.

Scientific studies based on known ovulation date (which is the most direct way of determining the actual start of a pregnancy) show that "delivery date" is actually a 37 day window if you look at women in general, though a particular woman will have a smaller window. Reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3777570/

Starting with LMP adds additional uncertainty (making the window larger), especially for women with irregular cycles, but even if you know the exact date of conception your normal delivery date window is about 5 weeks.

7
doubtfulttc•

This is a fascinating study! Thanks for sharing.

2
ovaries-b4-brovariesSTM | May 28•

I usually ovulate on day 14 of a 28 day cycle so the LMP math is pretty accurate for me.

With my first, my ultrasound dating exactly matched my LMP EDD, and she was born on that day.

4
thatnerdymummy•

My first was based on ultrasound, and he was born 3 days late. I had no idea when my LMP was because I was so irregular, however with this one, at the minute we're working off LMP. Well, the midwife is, I know when I ovulated so I'm working off that. I haven't had an ultrasound yet - first one next Tuesday - so we'll see what they say!

3
thevariablecauseOP•

Oooh please do let me know what the ultrasound shows! I’m super fascinated by all these numbers haha.

1
thatnerdymummy•

Me too! Though I have no idea what they mean!

1
dazedstabilityFTM 07/28/2018•

I didn't have a dating scan, but we went by what baby was measuring at the anatomy scan. Based on that, he was a day early. If I went based on lmp he would have been 4 days late. It makes sense since my cycle is longer than 28 days.

3
retardonarope•

So I only had sex once in my cycle, and had an app for ovulation/menstruation. So while I don't know exactly when the swimmers got to the egg. I know exactly the dates of sex & LMP.

There were two days difference between working out due date from sex and LMP. My ultrasound dated it as the day in-between! So all pretty close!.

3
tkinthewoods•

With my first I was due on the 20th per a dating scan. Went past my due date (common for first time pregnancies) and ended up induced with high blood pressure at 40+2. So I was close, but probably would have gone over a few more days w/o the induction.

My suggestion is to not obsess over the estimated due date because a lot can happen before and many go over. It becomes a fixation for you and others and can drive you a little crazy! Pregnant with my second and I tell people I’m “due in mid-October, but who knows?!”

Best of luck

2
thevariablecauseOP•

I’m not really obsessing over it my own due date, I’m just super fascinated by the numbers, if that makes sense, as well as the technology.

3
tkinthewoods•

Totally - it’s just hard not to obsess the closer you get. I have two weeks left and it is always top of mind no matter how hard I try!

0
b1cc13•

Dating scan at 8 weeks and my 12 week scan both put my EDD at LMP + 5. I went into labour spontaneously at 40 (scan EDD) + 3 and delivered at 40+5 and she apparently looked slightly overcooked, so EDD was prob pretty accurate for me. My normal cycle when it didn’t get messed up tended to be around 33-34 days as well, which is consistent with the scan EDD

2
frontbottomsbaby•

I had funky periods before pregnancy and my due date was ultimately based on a dating scan which put me at 8 weeks pregnant as opposed to 10 weeks based on lmp.

I gave birth at 38+4 and the nurses told me the baby actually looked slightly overcooked because his skin was a lot drier than babies who are born closer to their due date. So... Who knows 🤷‍♀️

2
mirandaleecon•

We relied on ultrasound with my last because my stupid phone erased all my notes on my cycle. I remember thinking that it seemed like it was almost a week off but could never remember exactly when LMP would have been or even the possible conception date was. My daughter was born at 41+3.

This time I know exactly when my LMP was and have a good idea when conception was. My due date is Apr 15th (which is coincidently my daughter's birthday) so I'll get back to you in Apr on how accurate it is lol

In all honestly, everyone is different. The EDD is after all just an estimate but your body knows when the right time is. I seriously obsessed about when I was going to have my daughter and it actually added a bit of stress to my last month only for her to be late anyway. This time I am just going to accept that it will happen when it happens.

​

1
thevariablecauseOP•

I’m really curious about this because I know the exact day my husband and I had the baby-making sex (when the actual conception was, of course, can’t be known for certain, but can’t be farther off than five days, or however long sperm survive). If we did 100% conceive on that day, like if we did IVF on that day instead of have sex, according to all the internet calculators my due date would be just a day before my ultrasound EDD. I just found it super interesting that the dates were all aligning, because everyone I know talks about how bad “pregnancy math” is lol. So I’m really just curious from an almost scientific point of view, if that makes sense.

That being said, I do get that a lot of it isn’t an exact science, and even those that do get a lot of interventions during conception could have babies born a few weeks off their due date.

3
Waffles-McGeeFTM Jan 05 2019•

I haven’t delivered, but my dating ultrasound and my tracking of ovulation with temping are also just a day apart

2
mimihihi•

mine are 3 days apart.

1
MrsCharmander#3 born 10/6•

I have very regular menstrual cycles and knew which date I ovulated. The LMP matched for my dates, and the ultrasounds always matched my what the LMP date said. Despite everything agreeing on a certain date, my first was 15 days early and my second was 10 days early. At this point, I would be surprised if my third kid stayed in until the due date.

1
fgn15•

I’d say it’s all a big guess. Here’s why, I was IVF. Literally, they knew the exact moment the kid went in, and STILL I had two EDD. One was based on transfer date (used by my IVF clinic) and the other based on measurement at 6 weeks (used by my ob).

In the end, the kid will come when it comes or the doctor says it’s gotta come. Use it as a best guess and leave it at that.

1
Pumpkinmama02•

I had a dating scan at 5 weeks for all of my kiddos because my cycle lengths are really wonky. My first came at 37+6 and my second came at 37+4.

1
peachysk8•

My due date was 6/10 based on LMP, 6/8 based on ultrasound, since it was so close they didn’t move my due date. I delivered 6/7.

1
27emeralds•

For my first, we went off of LMP and he was 1 day early (if they had gone from the ultrasound dating he would’ve been about 10 days late). For my 2nd, his due date changed based on the ultrasound date. From my LMP, the due date was 12/26 and from the ultrasound, the due date was 1/2. He was born 1/5. I’m now pregnant with my 3rd and didn’t have an LMP date to go off of as I got pregnant the first cycle after a miscarriage so our due date is from the ultrasound. This due date isn’t until March so I can’t tell you how accurate it will be!

1
uneekbean#2 March 29 | Team Blue •

I had my baby the day after my ultrasound due date.

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ntdnbs15|01|19 Team Blue! •

Can't say yet whether my current due date prediction is accurate, but: according to my LMP, my due date would've been the 25th of January. Dating scans predicted my due date as being January 15th, so ten days earlier! My cycles are usually pretty regular give or take a day, so that certainly was a surprise.

1
[deleted]•

My LMP gave me a due date of June 29th, they bumped it a few days earlier to June 25th based on ultrasound because she was measuring a bit bigger.

She was still 10 days early based on a June 25th due date or a full two weeks early based on the original due date. she was 7 lbs 9 oz. my periods were pretty regular and I had tracked everything on an app. I don’t think the dates were wrong, I think she’s just a big kid, and was ready to come out. She’s 15 months and still in the 97th percentile for height and weight.

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1
Silly__RabbitTeam Blue! •

With both of my pregnancies the difference between ovulation (based on OPKs and temping), LMP and dating it was all +/- a day. my first was born at 38+6, exactly a week early.

1