The baby can be measured as early as 5 or 6 weeks after the mothers last menstrual period. Measuring the baby using ultrasound is most accurate in early pregnancy. It becomes less accurate later in pregnancy. The best time to estimate gestational age using ultrasound is between the 8th and 18th weeks of pregnancy.

Can you tell date of conception from ultrasound?

The best way to determine your conception date is with a pregnancy confirmation ultrasound. Early pregnancy ultrasounds can determine the age of your growing baby and when you likely conceived.