Of all of these uses, dating the pregnancy is the most common reason to use ultrasound, particularly when the expectant mother cannot remember the date of her last period as in breast-feeding or irregular cycles.
When an ultrasound is performed, measurements of the head, abdomen, thigh, and amount of amniotic fluid are done. This creates error in that the baby will compute out to be further along than he or she really is. For instance, Accuracy of hookup pregnancy by ultrasound you normally have eight and nine pound babies.
Then your baby at 37 weeks will have bigger measurements than babies destined to weigh seven or eight pounds at birth. This may then indicate that your week baby is two weeks overdue!
Therefore, measurements taken later on, when babies begin to grow at different rates among pregnancies, yield increasingly inaccurate dating of pregnancy. Although the dating of pregnancy accuracy takes a dive, still ultrasound is indispensable for the other uses. Nevertheless, this measurement is fairly accurate. In the second trimester, past the first 12 weeksthe other measurements can be added.