12 doctors weighed in:

Why are ultraound edd more accurate than your LMP edd?

12 doctors weighed in
Dr. Jeff Livingston
Obstetrics & Gynecology
4 doctors agree

In brief: Not always true

Early in fetal life all babies grow at the same rate.
The longer into the pregnancy the more each baby grows slightly differently. Therefore, early in pregnnacy we can measure the size of a baby and very accurately predict the due date. Later on though, the sonographic measurements less accurately predict the due date.

In brief: Not always true

Early in fetal life all babies grow at the same rate.
The longer into the pregnancy the more each baby grows slightly differently. Therefore, early in pregnnacy we can measure the size of a baby and very accurately predict the due date. Later on though, the sonographic measurements less accurately predict the due date.
Dr. Jeff Livingston
Dr. Jeff Livingston
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Dr. Jose Bolanos
Obstetrics & Gynecology
2 doctors agree

In brief: Good Question

An lmp (last menstrual period) edd (pregnancy due date) is the most accurate if everything is normal and ovulation occured 14-16 days after the lmp.
Unfortunately, abnormal or delayed ovulation or missed ovulation are causes of inaccurate edd predicting. An ultrasound done in the first trimester of pregnancy will most accurately validate the lmp edd or invalidate it, hence the scan edd.

In brief: Good Question

An lmp (last menstrual period) edd (pregnancy due date) is the most accurate if everything is normal and ovulation occured 14-16 days after the lmp.
Unfortunately, abnormal or delayed ovulation or missed ovulation are causes of inaccurate edd predicting. An ultrasound done in the first trimester of pregnancy will most accurately validate the lmp edd or invalidate it, hence the scan edd.
Dr. Jose Bolanos
Dr. Jose Bolanos
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Dr. Craig Keathley
Obstetrics & Gynecology
1 doctor agrees

In brief: They aren't.

Determining due date is not exact regardless of the method used.
We are looking for the best estimate. A sonogram early in the pregnancy (8-10 wks) is an accurate method of dating a pregnancy, but still has a margin of error of several days. Later sonograms are less accurate. If the lmp edd is within the margin of error of the sonogram, the lmp date is the best estimate.

In brief: They aren't.

Determining due date is not exact regardless of the method used.
We are looking for the best estimate. A sonogram early in the pregnancy (8-10 wks) is an accurate method of dating a pregnancy, but still has a margin of error of several days. Later sonograms are less accurate. If the lmp edd is within the margin of error of the sonogram, the lmp date is the best estimate.
Dr. Craig Keathley
Dr. Craig Keathley
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1 comment
Dr. Peter Baumann
Common errors with LMP in my experience: 1) women don't know that the day the menses starts is the day that the clock starts ticking - they give doctors the day that the menses stopped; 2) women don't remember the dates of their menses correctly; 3) they have irregular periods and cannot discern what was a "real" menses. Worst case scenario: a combination of 1- 3.
Dr. Neeoo Chin
Fertility Medicine

In brief: Pregnancy dating

Lmp pregnancy dating relies on ovulation being on day 14, but some if not many women ovulate a few days before or after. First trimester ultra sound dating, especially first 8 weeks, is much more accurate by measuring the length of the baby correlating with the appearance of the heart beat.

In brief: Pregnancy dating

Lmp pregnancy dating relies on ovulation being on day 14, but some if not many women ovulate a few days before or after. First trimester ultra sound dating, especially first 8 weeks, is much more accurate by measuring the length of the baby correlating with the appearance of the heart beat.
Dr. Neeoo Chin
Dr. Neeoo Chin
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Dr. Padmavati Garvey
Obstetrics & Gynecology

In brief: They are not

Ultrasound based edd were established by doing ultrasound measurements on women who absolutely knew when they conceived.
Thus they are just as accurate as a very accurate lmp. Some women do not remember an accurate lmp.

In brief: They are not

Ultrasound based edd were established by doing ultrasound measurements on women who absolutely knew when they conceived.
Thus they are just as accurate as a very accurate lmp. Some women do not remember an accurate lmp.
Dr. Padmavati Garvey
Dr. Padmavati Garvey
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1 comment
Dr. Padmavati Garvey
Sometimes when you actuallly conceived is not exactly the time that you would expect based on your LMP or could be a few days after you have ovulated. The women they used to establish ultrasound measurements initially were women who had gone through invitro fertilization or women who had had sex only once in a given month, etc.
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