Which due date should I go with?


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According to my LMP (which I'm very sure of) my baby's due date is on Feb 9th.

My 12 weeks ultrasound said Feb 15th, but subsequent ultrasounds showed Feb 9th (same as my LMP).

I know it's a few days' difference, but which date is more accurate?
i would say your LMP.

i KNEW when mine was, but BOTH of my babies measured at least 2 weeks smaller than that. i had arguments with some intern dr's over it. it is perfectly possible that the baby is measuring larger for the age.

it should also be kept in mind that their measurements are AVERAGES.
Depends on who did the ultrasounds, but actually, I would tend to go with 12 week ultrasound as the more accurate predictor of those you mention.

LMP method assumes you have an "average" length luteal phase, whereas in fact this varies by +/- 2 days amongst individuals.

In early ultrasounds where the fetus is still quite small the variations in size amongst individuals are also not great, so it's actually a very good indicator. An earlier 7 week ultrasound would be generally an even better predictor.

Ultrasounds later in pregnancy show more variation in length and sizing of the baby in utero due to usual difference amongst the population, so you wouldn't tend to change your estimate of due date on those.
I would go with your LMP. I my case, I had IVF and had twins so knew exactly when fertilization took place and the scans sometimes had them with two weeks difference and weeks off the actual due date. Scans are not 100% accurate. Go with your feeling.
Actually according to LMP my EDD should be 1st March but since day one my OB has told me that my EDD is 8th March seeing the size of the baby perhaps???
Agree with beckveldman. LPM works only is you have the average 28 day period cycle, with ovulation on cd 14, and luteal phase of 14 days. Mostly people don't have that (At least I don't.. Although this time I did ovulate on cd 14 thanks to Clomid)

And also, early scan can give you a better estimate of your due date, as all babies grow in the same rate at first. Later it is hard to predict, as babies grow on their own rate.