How does an ultrasound determine your gestational age without the known last menstrual period date?

Answer by  11worker (86)

The fetal body measurements help to determine the gestational age of the fetus. Crown to rump length (at 7-13 weeks) is most accurate in determining gestational age. Fetal heart rates vary as well with gestational age at 6 weeks heat rate is about 90-110bpm, 9 weeks 140-170bpm, etc. In addition, polynomial equations using computer software determine gestational age.

Answer by  moonpie (84)

Determining gestational age with ultrasound is done by using measurement. Depending on how many weeks along you are, they may take measurements of the sac, crown to rump or biparietal diameter (diameter of the head), or a combination of these & other measurements to estimate gestational age, even weight. All without ever knowing the date of your last period.

Answer by  kellybean (72)

Ultrasounds can be used to estimate the gestinal age of a baby best in weeks 8 through 18. However, the baby can be measured as early as 5 or 6 weeks. The ultrasound will show the size of the baby and the doctor will estimate the age based on the size of the baby.

Answer by  Ali41 (1593)

In an ultrasound, the doctor or sonographer will determine your due date based on the size of the fetus and its features. For example, if the heart beat is just starting, then you would be some where in the six to eight week range of your pregnancy. The ultrasound dating is just an estimate.

Answer by  Roland27 (16334)

It's quite simple really. The Technician will measure the dimensions of the babies body and head. Based on the measurements they get they can tell how old the fetus is. It is actually a very accurate way to tell the age of the fetus, especially if you're not sure on the date of conception.

Answer by  ginat (0)

if you were 7 weeks preg would that make the fetus 5 weeks and did i concive around the 5 weeks and not the 7,im a little confused because if the fetus is 5 weeks does that mean i did not get preg 7 wks ago,by dates of ultrasounds,