A small but very positive study just released, “Noninvasive blood tests for fetal development predict gestational age and preterm delivery” has demonstrated the ability to determine gestational age with a blood test as accurately as early ultrasound (most reliable of any ultrasound).Click to see full answer. Beside this, how do you determine gestational age?Gestational Age by LMP is calculated from the first day of the last menstrual period. EDD by LMP is calculated by adding 280 days (40 weeks) to the first day of the last menstrual period. Gestational Age by US is measured by ultrasound (US) on the Ultrasound Date.Additionally, what is the difference between gestational age and fetal age? Gestational age is the age of the pregnancy from the last normal menstrual period (LMP), and fetal age is the actual age of the growing baby. Most references to pregnancy are usually in gestational age rather than fetal age development, but we have included both so it is clear what stage development is at. Keeping this in view, how does ultrasound determine gestational age? Ultrasound. The baby can be measured as early as 5 or 6 weeks after the mother’s last menstrual period. The most accurate way to determine gestational age is using the first day of the woman’s last menstrual period and confirming this gestational age with the measurement from an ultrasound exam.Can abnormalities be detected at 12 week scan?An early ultra-sound scan at 10-12 weeks can indicate major abnormalities such as anencephaly (absence of a brain) or missing limbs, and whether the foetus has Down’s Syndrome. A late ultrasound scan at 16-20 weeks can detect spina bifida, hare lip and certain heart defects.