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Dr. Chip
Dr. Chip, Doctor (MD)
Category: Health
Satisfied Customers: 28091
Experience:  Over 20 yrs of Family Practice
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Dr. Chip. I have a question about fetal ultrasounds. Would

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Dr. Chip. I have a question about fetal ultrasounds. Would it be possible for an ultrasound at 7 weeks to be off by 4-5 weeks? Would it be possible for a 12 week fetus to be mistaken for a 7 week fetus? Would it be possible for an 15 week fetus to be mistaken for an 11 week fetus via ultrasound?
Hi--before I get into specifics, is there a reason you ask?
Customer: replied 3 years ago.

I would just like to know if my ultrasound dating is accurate.

OK--but what you said above was a little unclear to me--can you tell me specifically what the situation is?
Customer: replied 3 years ago.

I was just wondering if ultrasound dating could be off a month in the first trimester?

OK--and we can continue after this but, no, not off by as much as a month. Perhaps off by from one to maybe two weeks, but certainly not a month.
Customer: replied 3 years ago.

Ok I was just curious. I was trying to figure out if I got pregnant in Jan or Feb. My EDD by multiple early ultrasounds is 11/12/13. I had an ultrasound at 7 weeks and 11 weeks (also at 14, 19, 21, & 27) that all gave the same due date. It is not an issue of paternity, but I was on medications on Jan & drank a lot, so I would feel better if the pregnancy did not result from this time. I had a period in early Feb.

OK--but with that information it would seem fairly certain you conceived in mid February so I would go by your last period and not by the ultrasounds and so you really have no need to worry here.
Customer: replied 3 years ago.

Well my ultrasonds and my period line up exactly. My periods are a little wacky & often irregular. I was just nervous and wasn't sure about accuracy. Aren't ultrasounds supposed to be more accurate than periods? Thank you for your help.

Actually the due date and the fetal age are determined by a combination of the last period, the ultrasound results, and blood work. I really don't thing you should have any concern here and I'm sure your baby is healthy and fine.
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