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A 25-year-old female asked:

How can conception date determined by early trans u/s done at 6 weeks 3days be accurate if you can still get pregnant w/in the 2 weeks of gestational age?

1 doctor answer1 doctor weighed in
Dr. Robert Crumb
Obstetrics and Gynecology 27 years experience
The size counts: 6 weeks is a historic term based on first day of last menses, with conception on the first day of week 2. Ultrasound measures size. Every pregnancy starts as a single cell. The closer to that point the image, the more accurate the estimate. At 6 wks 3 days the accuracy is about +/- 5 days. So if that is the ultrasound size the conception was 4 wks 3 days +/- 5 days prior.
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Last updated Sep 1, 2013


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