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A 29-year-old female asked:

can a 5 week ultrasound be off by a week or more like a couple days?

3 doctor answers3 doctors weighed in
Dr. Addagada Rao
General Surgery 56 years experience
Possible few days: Radiologist , interprets pretty accurately , may be off by few days not few wks, as the embryo will follow the clock like pattern , end of 4 , beginning of 5 wk you see gestational sac and fetal pole, speak to your doctor who has more information, good luck.
Dr. Amy Levine
Radiology 23 years experience
Ultrasound dating: First trimester ultrasound is accurate within 5-7 days. There is no test that can date conception more accurately than a 1 week window.
Dr. Joseph Accurso
Radiology 29 years experience
Ultrasound +/- 8%: Properly performed and interpreted ultrasound examinations have a variability of 8% plus or minus the measured dating. Given the dates in the question and assuming a high-quality ultrasound, i would suspect that last menses dating is inaccurate. Ultrasound dating at 5 weeks 0 days should have a 95% confidence range of 4 weeks 4 days to 5 weeks 3 days which is +/- 8%.

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Similar questions

Canada
A 32-year-old female asked:

At an ultrasound, what determines if you are 12 weeks or 12 weeks + 4 days? Are measurements this precise? And the accuracy correlates with your LMP too?

1 doctor answer1 doctor weighed in
Dr. Allison Urrutia
Obstetrics and Gynecology 14 years experience
Crown Rump Length: At twelve week on ultrasound, the sonographer measures the fetus' crown rump length (crl). This measurement is from the base of skull to tailbone. Ultrasounds at twelve weeks are accurate within 7 days. If you were 12 weeks by LMP and 12 4/7 weeks by sono, you due date would stay consistent with your lmp.
Punta Gorda, FL
A 25-year-old female asked:

Can an ultrasound be off by 14 days?

1 doctor answer1 doctor weighed in
Dr. Dwain Rickertsen
Family Medicine 36 years experience
Family practice : Usually they are pretty accurate. You could have another u/s to confirm dates.
United Kingdom (Great Britain)
A 22-year-old female asked:

Periods longer went from 28 to 33 day cycle & last 2 cycles were lighter. Ultrasound results fine. Doc says its likely environmental. Should i worry?

1 doctor answer1 doctor weighed in
Dr. Bryan Treacy
Gynecology 35 years experience
May be normal: Menstrual irregularity is common. Environmental stressors can induce changes in the hormones that direct the length of the cycle. A normal menstrual cycle usually runs from 26-35 days in length including the menstrual period. This cycle length is not concerning.
A 22-year-old female asked:

Im due september the 20th 2013 could I have conceived on 25 th november 2012 i went for ultrasound on 30th of january and i was 6 weeks and 5 days?

1 doctor answer2 doctors weighed in
Dr. Diane Minich
Family Medicine 37 years experience
No: By the ultrasound you would have conceived around the end of december.
Maryville, TN
A 24-year-old female asked about a 26-year-old female:

Can you use ultrasound to help determine paternity if sexual encounters are a month (30+) days apart?

1 doctor answer3 doctors weighed in
Dr. Robert Killian
General Practice 28 years experience
Early Pregnancy: The early pregnancy ultrasounds are used to get accurate dating of the pregnancy. This is where you can determine this answer.

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Last updated May 6, 2015
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