More accurate: u/s or lmp?

[GreenMomPhD]

Which is more accurate for predicting the due date, u/s or lmp?

I had an u/s around 8 weeks and my due date was estimated to be 7/25. If I use my lmp and default settings on a due date calculator (28 day cycle, luteal phase on day 14), the EDD is 7/23. However, while I don't know when I ovulated (after taking several rounds of Clomid, I decided not to worry about it so much), I know that my cycle lengths are much longer than 28 days. Therefore the due date would be more like 8/2-5. I went one week over my EDD with my first, so I am thinking it would be more like the beginning of August. Does that sound right, or should I just base it on the u/s?

[finnegansmom]

When was your LMP and when did you get your first BFP?
I would probably use the US date if you're really unsure, did you have a 20 week US as well? I tend to go later as well, and while I'm not against or nervous going over 42 weeks, I would like to truly know I'm at 42 weeks so I can opt for possibly some additional monitoring to make sure everything is OK.

[aikigypsy]

In this case, I would go with the ultrasound date, because it's later and sounds like it's probably closer (though maybe not close enough) to your actual dates (based on ovulation/conception).

[mistymama]

I would use the u/s date.

I also have long cycles, around 34 days. I knew when I conceived this time and adjusted my LMP to match my ovulation date - when we went for the early u/s the date matched my date exactly.

Early u/s are pretty accurate, I would use that. Esp since you know you have longer cycles, and probably didn't ovulate on day 14. That way they don't set your dd too early and start giving you induction pressure, etc when it's not time yet.

[GreenMomPhD]

When was your LMP and when did you get your first BFP?

My LMP was Oct 16, and the BFP was from a blood test at a fertility specialist on Nov. 17. I was told I didn't ovulate that cycle by my OB, so I didn't bother to take a home test!

I felt like I dropped this past Saturday, and today my OB said she was OA and low. I would love to go into labor anytime now, but since my first was late, I can't help thinking I'll be late again this time!!!

[tylerdylan]

I'm an ultrasound tech. Early U/S (less than 12 weeks or so) are VERY accurate at dating the pregnancy. Go with the date provided by the 8 week U/S. As baby gets bigger, U/S becomes less accurate.

[MaerynPearl]

Originally Posted by tylerdylan

I'm an ultrasound tech. Early U/S (less than 12 weeks or so) are VERY accurate at dating the pregnancy. Go with the date provided by the 8 week U/S. As baby gets bigger, U/S becomes less accurate.

Im not a tech, but from what I am told, an U/S by around 8 weeks should only be off by a day or two, not a week or more.

[rparker]

I *do* tend to have very regular 28 day cycles and with my last baby a first trimester ultrasound ended up being more accurate than my LMP. A 6 week ultrasound predicted October 13th and my LMP predicted October 11th. My daughter was born on the 13th. This time a 7 week ultrasound and my LMP agree on an EDD of October 11th...

[BlackSheepPDX]

Yes, the early u/s date you got should be your most accurate. However, I think particularly since you're wondering about a difference of two days, it's important to remind you that due dates, however accurate, are simply estimates of when you might have the baby. Very, very few people are going to have their baby on their due date, no matter how "accurate" the dating method.