Most Accurate Way to Determine Due Date W/o Basing It upon LMP?

Updated on July 25, 2010
M.T. asks from Herndon, VA
7 answers

Does anyone know the most accurate way to determine how far along in your pregnancy you are, if you don't know the exact date of your last period. My periods are somewhat irregular. Are there some ultrasounds that are more accurate than others? Or are there certain times in pregnancy when an ultrasound can be performed, which are better able to determine more precisely how far along you are in your pregnancy?

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answers from Columbus on

My Dr gives due dates based on the first ultrasound which he does around 12 weeks unless there is a medical reason to do it sooner. He told me the first ultrasound is the most accurate, I don't remember why.



answers from Dallas on

1st trimester u/s are much more accurate at predicting EDD.


answers from Dover on

The first ultrasound is usually the most accurate because it provides an estimate based on the size and development of the fetus. The earlier the ultrasound, the more accurate that estimate is. Early in pregnancy, all fetuses are basically the same size at the same stage. Later ultrasounds are not as accurate because when taking into account the fetus size it doesn't consider the size variations in full term babies...example: a full term baby that is born at just 6 lbs could be estimated at a later due date than a baby that is going to be born later but at 8 lbs.



answers from Seattle on

I had not a clue, having an average of 3-4 periods a year. So when I went in, kiddo could have been as little as 4 or as much as 20 weeks along. The measured him at 11 weeks, but gave my due date a "pad" of 2 weeks on either side So I was told "June", most likely, but possibly May or July... and they'd stress if he wasn't born by Aug1.

At least I never had to freak about "missing" my due date. Not with THAT durn big of a window. Really people? What you're telling me is Crocodile Dundee "In the Summertime"? LOL



answers from Spartanburg on

I didn't have a date for my last period when I got pregnant with my second child. THe midwife told me an ultrasound was very accurate for dating within 8 weeks of conception, and I was told that I was 7 weeks, 6 days along. My son was born on his due date and I have a consistent history of delivering within 24 hrs of my due date so it seemed like an accurate measure to me!


answers from Dallas on

I'd say an ultrasound that is done atleast before ten weeks. i didn't know my lmp with my son who was just born less than 2 weeks ago, and the one i had that showed me he was 6w5d was the most accurate (or the tech didn't know how to measure). they say essentially they grow at the same rate during that time.


answers from Provo on

At 20 weeks was my my first ultrasound they saw that my son was 2 weeks to small for my LMP. So they set my Sept 30 due date to Oct 15. I swore that I was due on the 30th. Nope. My little O popped out on Oct 14th. So I'd say just your first ultrasound, go by that.

Next question: Dating a Pregnancy with Ultrasound