Calculating Your Pregnancy LMP Or U S

10 Replies
yourtrish - May 17

Hi ladies...I just wanted to know which numbers you go by. My LMP was Nov.29th, which would make my baby's EDD Sept.5th, but according to my 20 week u/s, my baby measured to be due on Sept. 9th. Which date do you usually use as your benchmark?


HannahBaby - May 17

Its only 4 days so most doctors stay with the LMP date. 4 days isnt a big deal either way so it really doesnt matter. Espically at 20 weeks because some babies have growth spurts at different times y'know


Karen_Fletcher - May 17

prob the LMP, they normally give +/- 7 days to cover themselves with the u/s, or thats what iv found, cos mine are normally about the same, at the 12wk u/s they told me i was 1 day out in my counting, and if just gone on from there but it didnt change me EDD. hope this helps a little :o)


CKSAN - May 17

I have the same deal. based on LMP I am 20 weeks 6 days. But I had an ultrasound at 10 weeks that put me at about a week later. The Dr. still uses the LMP date. I do too. Sept 30 sounds much earlier than Oct 5th doesn't it? The earlier the better as far as my mind set is concerned!!


ThePezChick - May 17

I use my LMP. If I went by my baby's size I'd be off because he's measuring a little large for his "age". I know I my LMP was Dec. 29th and that I conceived on Jan. 13th. However, I consider myself to be 20 weeks along.


emilymalm - May 17

My OB is using my LMP even though my baby measured 9 days ahead. She said that ultrasounds can have a +/- of 14 days so she's going to leave by EDD as is.


charliepaulchloe - May 18

hi all, at my booking in scan they told me i was due 31st oct but since then i have had many appointments at midwife and they have give me a new date of 18th oct. at scan baby measured 6 wks 6 days but was actually 9 weeks. i am now huge and they think im gonna have a big baby as i was only small with my first child. my dates of 18th work out to my LMP and the measurements of the fundus work out the same.


yourtrish - May 18

Thanks ladies. Personally, I totally want to stick with the LMP...the sooner I get to meet little Audra the better! Mind you, I've heard that often, first time pregnancies go past their EDD, but deep down inside, I know the timing will be just right ... early, on time or late!


Trish# - May 18

My OB threw LMP out the window and strictly goes by u/s. Even if you know your conception date, it could take up to 10 days for implantation to occur and I think that has something to do with it. I agree that a few days is neither here nor their, and that EDDs are just a "guess" as the baby will come when s/he wants. My OB said that going by u/s measurements is much more accurate than going by LMPs, though. Also, women ovulate at much different times in their cycle so going by LMP alone can skew things...


Betul - May 18

U/S is definately more accurate than LMP. Like Trish said, women can ovulate at different times during their cycle and some women have 28 day cycles and some have may 29, 30, 32, cycles. some women ovulate on day 14, some on a later day in their cycle. Many women are inconsistent from month to month. Some months I have a 32 cycle, other months I had a 29 or 30 day cycle. Only with a OPK (ovulation prediction kit) could I be sure of ovulation. I know the exact day of conception so I go by that which correlates exactly with my u/s. LMP are fairly inaccurate because of so many variables woman to woman, but traditionally (before OPK and u/s)LMP was the only way to really determine due date.


Susan W - May 18

We're going by u/s. I conceived after a m/c and never had a period after that -- my LMP was October 27, 2005! (you should have seen the technician's face when I said that). I know exactly when I ovulated and conceived, and u/s has correlated exactly.



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