The point of the scan is to work out how many weeks pregnant you are. You may have calculated the length of your pregnancy from the first day of your last menstrual period (LMP). However, conception doesnt actually occur until around 14 days after your LMP, or later if your cycle is longer than 28 days.

Do ultrasounds measure from conception?

Fetuses grow quickly, and they also follow the same pattern of growth in virtually every case. That means that by measuring the size of the fetus and looking for certain distinguishing characteristics, an ultrasound can give an accurate estimate of when you conceived.

How accurate is conception date based on ultrasound?

The earlier the ultrasound is done, the more accurate it is at estimating the babys due date. Ultrasounds performed during the first 12 weeks of pregnancy are generally within 3 - 5 days of accuracy. The most accurate time is between 8 and 11 weeks gestation.

How does an ultrasound determine date of conception?

The best time to estimate gestational age using ultrasound is between the 8th and 18th weeks of pregnancy. The most accurate way to determine gestational age is using the first day of the womans last menstrual period and confirming this gestational age with the measurement from an ultrasound exam.