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Doctor insights on: Is Your Lmp Or Ultrasound Most Accurate

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If LMP and 12 week ultrasound correlate, would the u/s be considered more accurate since the LMP is known? Or is there still 1 week margin of error?

If LMP and 12 week ultrasound correlate, would the u/s be considered more accurate since the LMP is known? Or is there still 1 week margin of error?

LMP for dating : If in the first trimester, we go with the lmp unless the sono is over a week off. I we give the ultrasound date, but say "consistent with dates" the and still use the lmp date. ...Read more

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Dr. Michael Gabor
2,279 doctors shared insights

Sonogram (Definition)

An ultraound, also known as a sonogram, is a painless and relatively inexpensive imaging test that utilizes sound waves instead of ionizing radiation. There are no side effects. Ultrasound can give us two-dimensional, and in some applications three-dimensional, images of structures and organs in virtually any part of the body. In addition to diagnostic uses, such as evaluating abnormalities in the abdomen, pelvis, and breast, ultrasounds are commonly used to guide needle and catheter placement in a variety of surgical ...Read more


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How accurate is the due date with a sonogram at 15w3d?

How accurate is the due date with a sonogram at 15w3d?

Usually close. : Studies have shown that up to 20 wks gestation, ultrasound can vary by as much as 1.2 wks. Others have shown a 2 wk variaton between 18 to 28 wks, and 3 wk variation at greater than 28 wks. In a normal developing fetus, variations are usually secondary to the experience and expertise of the technologist, position of the fetus, and the accuracy of the measurements. ...Read more

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How accurate/reliable is a LMP by ultrasound if the patients LMP was unknown?

Pregnant?: I assume you are pregnant. Early transvaginal ultrasound is very accurate and giving a proper gestational age for you pregnancy. From that age a due date is given and an "lmp" date is given even though you may not have actually had a menstrual cycle at that time. ...Read more

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If last LMP is not known would a ultrasound measure sac in early pregnancy to match gestational age ?

If last LMP is not known would a ultrasound measure sac in early pregnancy to match gestational age ?

Yes: An early transvaginal ultrasound can accurately estimate the gestational age within a couple of days. In the first trimester, there is very little biologic variation in size. If the embryo is present, the "crown-rump length" is routinely measured and used to determine the gestational age. Also, the mean diameter of the gestational sac gives a reasonable estimate of age. ...Read more

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Confused on due date. Late in pregnancy which is more accurate, ultrasound or fundal height?

Confused on due date. Late in pregnancy which is more accurate, ultrasound or fundal height?

Earlier info: Your due date shouldn't change in late pregnancy. It is established by info about your last period and earlier ultrasound. ...Read more

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How accurate is an ultrasound due date estimate?

How accurate is an ultrasound due date estimate?

Best on earlier u/s: Ultrasounds use composite data obtained during the exam to determine an EDD (estimated date of delivery). This date will also have a +/- number of days giving an accuracy range. First trimester ultrasounds are accurate to within about a week, second trimesters estimates are accurate within about 2 weeks, and third trimester scans about 3 weeks. ...Read more

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Is first ultrasound or the second more accurate?

Is first ultrasound or the second more accurate?

Ultrasound dating: The first. First trimester ultrasound is accurate within 5-7 days. 2nd trimester ultrasound has accuracy of +/_ 2 weeks. Lmp dating also assumes a 28 day cycle. There is no test that can date conception more accurately than a 1 week window. Due date is based on lmp unless us off by more than 1 week 1st trimester or 2 weeks in 2nd. ...Read more

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What changes a due date? And why is the first trimester ultrasound more accurate than the second trimester ultrasound?

What changes a due date? And why is the first trimester ultrasound more accurate than the second trimester ultrasound?

Ultrasound dating.: First trimester ultrasound is by far the most accurate in determining the precise due date (+/- 3-7 days, depending on exactly when it is performed). Second trimester sonograms are less accurate but still helpful in pegging down the due date within +/-7-12 days. Third trimester scans are not very accurate in dating the pregnancy, as growth varies (+/- 14-21 days). Menstrual dating is not very good. ...Read more

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Which is more accurate at detecting the baby's due date? The five or eight week ultrasound?

Which is more accurate at detecting the baby's due date? The five or eight week ultrasound?

Ultrasound dating: First trimester ultrasound is accurate within 5-7 days. 2nd trimester ultrasound has accuracy of +/_ 2 weeks. Lmp dating also assumes a 28 day cycle. There is no test that can date conception more accurately than a 1 week window. Due date is based on lmp unless us off by more than 1 week 1st trimester or 2 weeks in 2nd. ...Read more

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Is the age shown on an ultrasound measured from LMP or conception? The US said 5w1d. If this is from LMP, conception would be after I got a pos. test

Is the age shown on an ultrasound measured from LMP or conception? The US said 5w1d. If this is from LMP, conception would be after I got a pos. test

From LMP but..: ...If the sonographic dating was obtained from measuring the "mean gestational sac size", its margin error may be wide and it may be inaccurate. If it was determined from the average of 3 measurements of a "crown rump length" by a certified experienced sonographer, it is more reliable and precise. A repeat scan in a few weeks may be valuable. ...Read more

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What week in pregnancy is most accurate in ultrasound dating?

What week in pregnancy is most accurate in ultrasound dating?

6-8 weeks: Ultrasound dating is most accurate early in the pregnancy using the crown-rump length (crl) of the small fetus. The measurement can be done starting around 6 weeks. While crl can be used for dating until 12 weeks, it is most accurate during 6-8 weeks when the accepted error is only about 3 days from actual date. ...Read more

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What is best to go by edd LMP or edd ultrasound?

Depends: If the first ultrasound was done in the first trimester, especially 7-10 weeks, there is no doubt that the sono is best. After the mid 2nd trimester it's anyone's guess. ...Read more

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Which is more accurate at determining the date of conception? A 5 or 8 week ultrasound?

8 week: The most accurate measurement for dating is the crown-rump length at between 7 and 13 weeks gestation. ...Read more

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Which gestational age is more accurate, LMP based or ultrasound one? By LMP i am 27weeks and 4 days.ultrasound says 28 weeks

Which gestational age is more accurate, LMP based or ultrasound one? By LMP i am 27weeks and 4 days.ultrasound says 28 weeks

Gestational age: Your LMP is usually more accurate than ultrasound especially at 27+ weeks. Ultrasound is more accurate in the first trimester and gets less accurate the further along you get in the pregnancy. ...Read more

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Does ultrasound accurately measure pregnancy or just go by lmp?

Does ultrasound accurately measure pregnancy or just go by lmp?

Ultrasound is better: Ultrasound is certainly a better estimator of gestational age than lmp in the first trimester and the first half of the pregnancy. The lmp is often off. Many women will experience some spotting at 4 weeks and consider that a menstrual period. The ultrasound can also evaluate the fetus and placenta and detect potential problems early. ...Read more

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Embreo transfer or ultrasound is due date more accurate?

Embryo transfer: Embryo transfer would be the ultimate gold standard for gestation age.The number of days since conception of the transferred embryo (3-5 days) would be known so the precise time of conception would be available so the estimated due date could be more precisely estimated. ...Read more