Accuracy of ultrasounds for dating
You can estimate your date of ovulation and conception from the length of your menstrual cycle if this is fairly regular.The most consistent part of the cycle is the second half after you ovulate.An image of your fetus will appear on an accompanying computer screen and while looking at this image, the technician will take some standard measurements from different angles and listen for a heartbeat.Don't worry: This type of exam is painless and risk-free, and seeing your baby for the first time will likely be an enjoyable experience.However, you could have conceived on day 12 or 13 if ovulation was earlier, or days 15 or 16 if later.So, by this example you can understand you have a five day window during which you could have conceived.And as long as the repeat ultrasound shows consistent growth and there are no signs of problems, there is no reason to be concerned if your doctor changes your due date.
You may have simply conceived earlier or later than you thought you did (which can happen if your cycle is at all irregular or if you remembered your last menstrual period date incorrectly).
Just wanting to know if any others have had an EDD from a scan that was different to the EDD calculated based on their LMP (last menstrual period).
Which was correct in the end – the LMP due date or the estimated date of the scan?
Every pregnant woman wants to know her due date, and a due date that is calculated from her last menstrual period often doesn't match the due date that is estimated by her first ultrasound (also known as a sonogram).
During an ultrasound, a technician will spread a warm gel over the lower part of your abdomen and then press a tool called a transducer against your belly to examine your fetus using sound waves.