Dating a Pregnancy with Ultrasound

I had two ultrasounds and both dated my baby exactly 3 days before my due date based on my last period and she was born 3 days after my due date, so only off 6 days.

They are very accuarate, but a baby will arrive when the baby pleases LOL. My daughter's due date was May 7th and we delived on May 2nd. My son was Nov. 23rd and we delivered Nov. 7th (so you have about a 2-3 week window). Don't schedule anything big in that window and you'll be fine - just be ready to go! And by the way congrats!!! How exciting!

I had the same thing with my second. I never had a period between having my first and getting pregnant with the second. I had 2 ultrasounds (one at about 8 weeks and one at about 20 weeks) and both put my due date April 12th. My daughter was about a week early. But I'd say that ultrasound due dating at the early stages of pregnancy are pretty accurate.

They are pretty accurate, but the later you get into your pregnancy the less accurate they become with regards to due date.

Try using a pregnancy calculator (here's a link to just one I found online, I'm sure there are many: http://www.americanpregnancy.org/duringpregnancy/pregcalc..., to get an idea of when you are due before you go into the ultrasound. You have to know the first day of your last period and the average length of your cycles to get the most accurate prediction.

The reason they measure all of these different things during an ultrasound is because babies predictably grow at the same rate when in early development. From our experience, they are so accurate the technician could tell the original due date given to us by our nurse practitioner was wrong by about a week. That being said, the number I've read is that only five percent of babies born are born on the estimated due date given early on in the pregnancy. Some come early, some come late.

I've been pregnant twice and had a total of 3 ultrasounds, so I think I'm qualified to at least give my opinion on the issue. With my first daughter, I was going to a birth center and they didn't do ultrasounds. But I really wanted to find out the sex of my baby, so I did the easy thing: I went down to Mexico and got one. Now, Mexico was only about 15 minutes away, and it only cost me about $30 or $40, and I found out I was having a girl, so it was definitely worth it. The only problem was that when I got the results back, the guy put the due date about 3 weeks earlier than we had originally estimated. This ultrasound was taken at about 5 1/2 months--later than is usually done for dating, but I wanted to make sure we could determine the sex!

Now, I knew when my last period was. I am dead regular (I can predict when my period will start 3 months in advance to within 1 day), and I had been charting my basal body temperature (to try NOT to get pregnant--we figured out where we had gone wrong later), so I pretty much knew the date I had conceived. So I really didn't believe the due date. But I went ahead and gave the results of the ultrasound to the midwives at the birth center so they could see it.

When they saw the discrepancy on the due date (the only abnormality, thankfully), they ordered another ultrasound at the local hospital. So about a month after the first one I went and had a second. Within minutes of starting the guy commented that it seemed the baby was further along than my due date indicated. And they put the due date almost a month earlier than the original one.

So, based on this, the birth center moved my due date up and began treating me as if I were a month further along than I had been. But I began to complain. I KNEW I hadn't gotten pregnant in December. And I knew something else. A birth center will only deliver a baby between 37 and 42 weeks, or something like that. If the original due date was correct, then the baby probably wouldn't be born within 2 weeks of the new due date, and they would send me to a hospital to be induced or something, which would give an early baby (not premie, but early, and who wants to be induced if they don't have to be? I was induced at 42 weeks, and my mom tells horror stories about it).

So I started complaining big time. I brought my chart to the birth center so they could look at it. I reminded them of when I first felt the baby move, and of how they couldn't find the heartbeat at a certain visit (if I was really that far along, wouldn't they have heard it by then?), and anything else I could think of. So finally one of the midwives decided to try to feel the size of the baby. After feeling it, she said, "This doesn't feel like that far along. If you can wait, I'm going to get the senior midwife to check you." So I waited, and the senior midwife checked me. It took her about 15 seconds, and she said, "This baby isn't big enough to be that far along. I'm putting your due date back to the original one." I breathed a sigh of relief!!!

My daughter was born 2 days before the original due date, and she wasn't early or late. So the ultrasound was way off.

However, several people told me that at 5 or 6 months, it's really hard to date by ultrasound. It's not very accurate. They said it's more accurate earlier, though.

Well, I got pregnant again this spring, and went back to the birth center. The senior midwife had retired and they had someone new running the place, and she figured that since Medicaid would pay for it, if the mother wanted an ultrasound, why not authorize one so she could have it? So I opted for one (I wanted to know the sex this time, too). She said the ideal time would be between 18 and 22 weeks, if I remember correctly, and so we scheduled one, I went and had it. When we got the results back, I saw that they had put the due date only one day different from the original one. So this one was very accurate. No stress.

So in conclusion... the later the ultrasound, the bigger the margin of error when it comes to dating. In your case, I would say it should be pretty accurate. Of course, the due date is really the ESTIMATED due date, because only about 1 in 20 babies are actually born on their due date, but it should be pretty accurate. Of course, other milestones like when they heard the heartbeat and when you felt the baby kick and other things will help confirm it. Talk to your caregiver about it. They will surely put your mind at ease. :)

Usually in the earlier parts of pregnancy they are rather accurate. Of course keep in mind that could still mean two weeks off.

It is plus-minus 2 weeks but may be you can remember the exact date that might happen and be more accurate. I knew the date, so it was very easy to tell accurately the due date, the contractions started exactly on the due date. Good luck!

They are typically very close and that is why they do the first ultrasound to calculate dates. This is very important also if you do not know your LMP and it sounds like after your 6month old was born, your periods were light or never happened. So it should be pretty much on target for you. Best of luck, WOW you will have your hands full.

Dear P.;
From my experiences..the ultrasound was very accurate..
It gave me a due date of the month and date due and by that very day I had, had baby by early morning of same date.You might try several ultrasounds for the most accurate..depends on dr. also..some will do more than one.
But at this time I would go with the given date..
Many Blessings;
C.

I had three ultrasounds to date my first pregnancy. One determined JULy 15th as the due date, one the 16th and one the 18th. My son was born on the 18th, so I think it's pretty accurate.

Amazingly enough - they are pretty accurate. When I got pregnant with my son - I had a weird period a week and half before I was suppose to start the month before my missed period. I thought they were wrong, but they had my due date set and I delivered 3 days early. So, point is - they are pretty accurate.

Dating a pregnancy in the first trimester by ultrasound is very accurate within a week I believe. The farther along in the pregnacy the less accurate the dating becomes as babies vary in size

They are fairly accurate. Can you schedule a hair appointment around them, no. But you'll be within a 2-3 week window. Babies get here when they get here. They more often than not arrive on your 'due' date, but their date, yes. Congratulations!!

Last year I had a miscarriage and then got pregnant right away. We had to use an ultrasound to date it since I did not have a period after the miscarriage. The due date they gave me then was July 13th. I ended up having him on July 10th.

The dates are more accurate when the ultra sound is done earlier in pregnancy.
So it sounds like that is your due date.
Please keep in mind that it is still an estimate of the date. That you can deliver 2 weeks before or 2 weeks after. But yes you have a better chance of going into labor closer to that date.
I hope that this helps
B.

sorry this is late, i was board and looking through old messages..
I've had two babies and after i delivered #2 a nurse explained something to me that made so much sence.

I had my first child 10 days past due and my second was late as well. The nurse asked me about my monthly cycle.. if it was exactly 28 day or more. I thought about it and it was closer to 30/31 days or more. ultrasounds are based off developement. but my cycle makes it have something to do with my being prego longer than most. I remember she gave me a good explination that i'm sorry i don't remember the exact reason. maybe ask your ob/gyn if they have heard this or can exactly explain it.
both my girls were a week late and it took 3 days to induce me.. my body just loved being prego and wouldn't give up the girls.. lol
so if when i do decide to have #3 (soon hopefully) I know to expect to be a week late at least.
www.babycenter.com is a fantastic way to track your pregnacy

I had one at 8 weeks and another at 20 weeks that both predicted the same day, and i went into labor on my due date (even though i didn't deliver untill the day after).