Due Date according to LMP vs. U/S Measurement

sylvia1023 · August 2011

We all know that doctors give you a due date according to your LMP, but I keep seeing that when mommies go for their checkups, they are measuring further along. Is this really possible? If it is, does that mean the baby is growing extra fast? Why is that?

I have my 1st appointment tomorrow and I will be 6w2d...I wonder if it's acurate?

pensparade · August 2011

I had a huge mix up with preg. #1 over LMP = Due date which was NOT accurate. So IMO, go by the u/s.

adamstodrake · August 2011

Some people may have ovulated earlier or later in their cycle than day 14, which is what an EDD is based of off (a 28 day cycle). For example I ovulated on cycle day 16, so the EDD based on my LMP would be 4/27, when in actuality a 4/29 EDD based on ovulation is really more accurate. Not many women know exactly when they O though, so the first EDD is given based on LMP. The u/s will just give you a more exact measurment. From what I understand though, they tend to line up with when the woman ovulated. Oh! And more than likely an EDD wouldn't be moved unless there is a +/- 7 day discrepancy.

Have fun at your first appointment!

LilyPotter218 · August 2011

I am lurking but have some experience with this

I charted and know I ovulated late, on CD23, not the "norm" 14. When I was measured at my first u/s I actually measured a few days ahead of this, but still 6 days later than LMP (assuming a CD14 ovulation). BUT, since it was within a week of LMP they will not change my due date.

Ticker is counting down to my due date, but in reality I am only 9w3d along. This is why I often lurk here I am a lot closer to early April than I am to a lot of the March mommas as far as weeks pregnant are concerned.

I figure once I am out of first tri the 6 days won' t matter as much and Ill just go with what my OB is using...

TheOriginalSP · August 2011

Most doctors go by LMP even if your cycles aren't 28 days...however if you know when you ovulated, some doctors will go by that date.

With my last pregnancy I know I Oed on CD8 so I knew when my EDD was based on that. My doc said "fine with me" and when I went in for my anatomy scan at 20 weeks baby was measuring almost exactly that. I think she was maybe 1 day ahead on growth.

And like pp said, unless there is a week or so discrepancy, most doctors wont even touch your due dates.

shouldbworkin · August 2011

My OB doesn't go by the LMP, except at the beginning when they're trying to figure out when to draw blood or do a dating u/s. I suppose if you said your LMP was a long time before when they expected they wouldn't even use that date. I had my EDD changed by 2 days with DD b/c she was measuring smaller at the u/s. Turns out I O'd later than I thought. I'm pretty sure that happened this time too and should get my "official" EDD next week at my next u/s.

lj_n_tj24 · August 2011

If I go by my LMP I would be 19 weeks by now but due to PCOS and very irregular cycle there's no way to tell but the u/s. Since I have PCOS and period is MIA most of the time I never know when I ovulate, if I even ovulate. My period regulated beginning of the year. I got AF in Jan, none in Feb, then March again then April then it was MIA again in May/June/July only to find out I'm KU. I charted on and off so I can't even go by that, I did POAS every month since AF was MIA and every month including July 26th was a BFN until July 30 came! what a big surprise I got a BFP! So yeah can't always base it on LMP. I'm now 7wks 4 days.

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