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How accurate is an Ultra-sound at determining how far along a pregnancy is?
Asked by: brenda5120
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A young lady who had a one night stand with my son a few months ago has come to him and told him that she's expecting. She's said that the child is either his or her ex-boyfriend whom she was also with one week after her encounter with my son. Here's the deal... The ultrasound was taken on July 23rd and states that she is 9w3d. I'm assuming that means 9 weeks and 3 days into the pregnancy....She and my son had their encounter on Friday May 16th. She claims that the night spent with her ex-boyfriend was the following Saturday which was May 24th. When I count back 9 weeks and 3 days from July 23rd, the date is May 19th. Two days after she was with my son and 6 days before she claims to have been with her ex.
Are the dates calculated on the ultrasound photo accurate? To within a week?
Are the dates calculated on the ultrasound photo accurate? To within a week?
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From what I know, ultrasound technology is usually only accurate to within about two weeks. They determine the date of conception based on the development of the fetus, so if this fetus is not "average" developing faster or slower than most, the date will be less accurate. In fact, they also ask the mother when she thinks the fetus was conceived, and may even base her expecting date off of that. You may want to remind your son about the importance of birth control....
Answer Date: 03:16pm 08/25/08
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Within the first trimester scans are accurate to within 2 days calculated by the crown rump length. BUT pregnancy is dated from the last menstrual period NOT the point of conception which will be two weeks after that on average (ovulation occurring mid cycle). In other words it is not possible to be one week pregnant. You need to count back 7 weeks 3 days, not 9 weeks 3 days.
Source: I'm an Obstetrician
Answer Date: 03:02pm 08/26/08
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