Accuracy of ultrasounds for dating
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.
If the ultrasound date is within seven days of your LMP date, we would stick with your LMP date.
Ultrasounds done later in the pregnancy are less accurate for dating, so if your due date is set in the first trimester, it shouldn't be changed.
If an ultrasound date in the first trimester differs from your LMP date by seven days or more, we would go with the ultrasound.If you can determine that day, you will come close to identifying your date conception.There are various ways to estimate the day of ovulation.If your first ultrasound gives you a due date that is more than 1.2 weeks away from what was expected, there is a good chance that everything is still fine.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).