ultrasound estimation of gestational age
The baby can be measured as early as 5 or 6 weeks after the motherâs 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. The most accurate way to determine gestational age is using the first day of the womanâs last menstrual period and confirming this gestational age with the measurement from an ultrasound exam.