Thread: due date confusion!

i plan to ask this at my next appointment, but figured I'd ask you ladies in the meantime. Lurkers welcome!!!!!!


I know for sure my conception date. That date gives me a due date of Dec 13. After my 9 week ultrasound they changed it to Dec 12th. Those dates are so close together that it really doesn't make a difference.


Today I had a repeat anatomy scan because they didn't get all the pictures they needed at 20 weeks. They measured his femur, abdominal and head circumference. They were all measuring 26-27 weeks. They changed my due date to Dec 6th!!!

What is more accurate, a calendar date or the ultrasound date? I KNOW his exact age because we know the day of conception, does being bigger necessarily equate with being born earlier? DS1 was 95 percentile for length, and over 100% for head circumference at birth and he was a week LATE.

I guess basically I'm not getting my hopes up that he will be a week early... but I'm certainly curious!

I have heard that ultrasounds at this point in pregnancy are NOT accurate for dating. It's only the very early 1st trimester ones that are accurate.

FWIW, when I was pregnant with DD, I knew my exact conception date, and the EDD based on that was July 10. After my 18 week u/s, based on her measurements, they guessed a new EDD around July 18-25ish (some body parts were measuring farther behind than others). Anyway, she was born on July 9, right on time.

So I wouldn't pay any attention to a date changed at this point, personally.

I would stick to your original date espcecially if you know when you conceived. As far as I know, baby could measure a little ahead right now but a few weeks from now, might measure a little behind!

Babies come in all sizes! It's my theory that they will come when they want to, so I would stick with your conception date too, but be ready early just in case!

Originally Posted by .hilary.

I would stick to your original date espcecially if you know when you conceived. As far as I know, baby could measure a little ahead right now but a few weeks from now, might measure a little behind!

I agree.
At my perinatalogist u/s last week, they stated that the overall measurement could be off by plus or minus 10 days, and each individual measurement (abdomen, head, etc.) has its own standard deviation of how much it could be off. I would stick with the original due date you were given. HTH!

You know what makes Dec 6th even more attractive? It's the feast day of St. Nicholas! I know the little man will show up exactly when he's supposed to. Too bad measuring big doesn't make them come any sooner

I would be surprised if the midwives change my date based on the radiologist's report. I think they will stick with Dec 12-13th. That is my REAL due date!

I have heard that they really aren't supposed to change your due date based on measurements from later scans--there is too much variation due to genetics at this point. A bigger baby will not necessarily be born earlier, since some babies are big at 37 weeks and some are small at 41 weeks. The due date is just a guess, anyway. I think I remember reading that only 5% of moms go into labor on their due date.

The purpose of early ultrasounds is mainly for dating procedures. Like others have said, there are too many variables at this point. How awesome would it be if Nicholas was born on Dec 6th though?

BTW- I think you are going to LOVE to sing the Christmas song "Jolly Ol' St. Nicholas" from now on. I know I love all the Chirstmas songs that say Nicholas in them now

I agree with PP - scans at this point aren't accurate.

When I did IVF I knew the exact day (and time) of conception and I knew the day I got pg (after transfer) but there was a HUGE descrpancy in my due date - from Nov 7 (my RE's calculations) to the 1st u/s which put me at Nov 10th and then my first OB appt at 12 weeks put me at Nov 20. Labor started on Nov 9 - I had him on Nov 11. I think the 1st u/s is always the best.

My baby was measuring bigger at my 20 week US, and they thought maybe Dec. 2 was my due date, but in talking to my midwife, she is sticking with the 5th or 6th, and their notes said that too (from the U/S), so I am sure they probably won't change it.