Question 1

if ultrasounds date from conception, then why did the sonographer tell me i was exactly as far along as my lmp says? edds were the same as well.

Accepted Answer

A common confusion: By convention we count the number of weeks of pregnancy as being from the date of conception plus 2.  Historically this is because the LMP is much more clearly known than the date of conception, which on average occurs 2 weeks after the lmp.

Question 2

i had my period on april 9th. my periods are fairly irregular by a week or so. my ultrasounds measure two weeks behind my lmp due date. i've had one done at 5wks (too small to tell), 6wks5dys, & 19wks. they all gave me the same due date by except 2 days.

Accepted Answer

Use ultrasounds: Your ultrasounds all give you the same due date within 2 days.  There is absolutely no reason to think that the calculation using your last period is going to be more accurate.

Question 3

is lmp more accurate than early ultrasound?

Accepted Answer

No: Early sonograms are more accurate than lmp.

Question 4

what does it mean whenever lmp date and ultrasound matches to the exact day?

Accepted Answer

: It is normal. Please note date of delivery is plus or minus two weeks from the LMP or the ultrasound estimate of the duration of gestation.
Get regular antenatal care.
Wish you good health and a healthy baby!

Question 5

if my first ultrasound was off by one day compared to my lmp what does that mean?

Accepted Answer

Nothing: That difference is of absolutely no significance and this is an excellent confirmation of your dates.

Question 6

which date is likely to be more accurate, the ultrasound date or the lmp date of delivery?

Accepted Answer

Neither: Ultrasounds have an accuracy "rate" of plus or minus 10-14 days depending upon when it was taken in the pregnancy. Small for gestational age or IUGR (intrauterine growth retardation) fetus' can also make the ultrasound unreliable. LMP dates are often notoriously inaccurate do to poor dates  record keeping.  An OB MD uses a combination  of  signs to  better estimate dates of delivery.(EDC)

Question 7

how do you know if your due date is accurate? (ultrasoud, multiple ultrasounds give same date, lmp, etc?)

Accepted Answer

Last cycle: If you have regular monthly cycles, and know your last cycle, this is a good standard to determine your due date. If you are unsure if your cycle, then you will be dated by an u/s. If the first u/s was performed in your first trimester (before 12 weeks), this will determine your due date. It will not change, regardless of other u/s obtained later, b/c due dates become more and more inaccurate.

Question 8

my ultrasounds date back to my (estimated) date of conception rather than the first day of my lmp. is this normal?

Accepted Answer

Yes: Most obstetricians will use your LMP to determine your probable date of conception.  This is the more appropriate starting point for dating your pregnancy.

Question 9

how accurate are ultrasounds at 12 weeks? on march 4 i was told 13w when i shouldve been 12w based on lmp. she said it could a week off

Accepted Answer

Fairly accurate: in general when approximating due dates the earlier the ultrasound the better and most accurate, if you had normal periods prior to pregnancy, i would use your due date from you lmp. further investigation is usually warrent at 12 weeks if your us edc is more than 1.5 weeks difference than the LMP on us at 12 weeks, good luck

Question 10

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?

Accepted Answer

+/-1 week.: First trimester sonography is more accurate than even certain menstrual dates due to inherent variation in ovulation. The degree of accuracy at 12 weeks is within a week of the true due date. Take Folic Acid 1-5 mg daily and good luck!

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Doctor answers about:

Lmp and ultrasound are the same

A member asked:

If ultrasounds date from conception, then why did the sonographer tell me i was exactly as far along as my lmp says? edds were the same as well.

A member asked:

I had my period on april 9th. my periods are fairly irregular by a week or so. my ultrasounds measure two weeks behind my lmp due date. i've had one done at 5wks (too small to tell), 6wks5dys, & 19wks. they all gave me the same due date by except 2 days.

A member asked:

Is lmp more accurate than early ultrasound?

A member asked:

What does it mean whenever lmp date and ultrasound matches to the exact day?

A member asked:

If my first ultrasound was off by one day compared to my lmp what does that mean?

A member asked:

Which date is likely to be more accurate, the ultrasound date or the lmp date of delivery?

A member asked:

How do you know if your due date is accurate? (ultrasoud, multiple ultrasounds give same date, lmp, etc?)

A member asked:

My ultrasounds date back to my (estimated) date of conception rather than the first day of my lmp. is this normal?

A member asked:

How accurate are ultrasounds at 12 weeks? on march 4 i was told 13w when i shouldve been 12w based on lmp. she said it could a week off

A member asked:

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?

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