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Conception Dates

How accurately can an ultrasound determine the date of conception?


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2015-07-15 21:38:21
2015-07-15 21:38:21

Ultrasounds measure the size of the fetus to predict a due date and are usually very accurate, within two weeks, so I would safely assume that it would not be off by five weeks. You can ask your doctor, it won't be the first time he or she has answered that question,I promise.

Also it depends on when the U/S is. U/S before 12 weeks of pregnancy are very accurate, plus or minus 2 weeks. After that there are more varibles, babies grow at different rates so they are not as accurate.


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For about the first 10-12 weeks all babies grow at about the same rate so term date can be calculated fairly accurately, you then count back 38 weeks for the date of conception. After 12 weeks babies may not all grow at the same rate so it becomes less accurate.

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Conception date is based on your last ovulation cycle prior to when you didn't get your period. But this can be incorrect if you didn't conceive when you was ovulating. Alternatively you can have a ultrasound scan which will give you a conception date but this can be off by 5 days.

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You can use a pregnancy conception calculator to determine when your baby was conceived. In order to find out your pregnancy conception date you need to know the date of your last menstrual period, the average length of your menstrual cycle and the average length of your luteal phase. Knowing the length of your luteal phase is very important to accurately determine the conception date.

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An ultrasound will determine the date of conception by measuring the fetus. You conceived somewhere between March 23 and April 24. It is difficult to pinpoint the exact date of conception this way without an ultrasound to measure the fetus.

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I am guessing you mean that you want to know your date of conception? It really depends on a couple of factors. If your normal periods are regular, you can be fairly accurate with conception date within a couple of days. Count back 14 days from when your period was DUE (ie but didn't come because you were pregnant) and this will be around the time of conception. Conception date will be within two days either side of this date. If you are pregnant now, an ultrasound will tell you very accurately what your conception date is. As long as you have an ultrasound within the first 10 weeks - the earlier the better. An experienced ultrasonic person can tell you down to the day - ie six weeks and three days.

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