How accurate is an early dating ultrasound?
A dating scan is an ultrasound examination which is performed in order to establish the how accurate is dating ultrasound age of the pregnancy. Most dating scans are done with a trans-abdominal transducer and a fullish bladder. If the pregnancy is very early the gestation sac and fetus will not be big enough to see, so how accurate is dating ultrasound transvaginal approach will give better pictures.
Dating scans are usually recommended if there is doubt about the validity of the last menstrual period. By 6 to 7 weeks gestation the fetus is clearly seen on trans-vaginal ultrasound and the heart beat can be seen at this early stage 90 to beats per minute under 6 to 7 weeks, then to beats per minute as the baby matures. Ultrasounds performed during the first 12 weeks of pregnancy are generally within 3 - 5 days of accuracy. The most accurate time is between 8 and 11 weeks gestation. This is because the fetus is growing so quickly that there is a big difference in size from week to week.
However, the accuracy of the ultrasound examination is always dependent on the skill of the sonographer and the quality of the equipment. Usually the expected date of delivery EDD or EDC is calculated from your last menstrual period - if the early dating scan calculates the EDD to be within 5 days of the EDD from your last menstrual period.
The EDD from the early dating scan is used - if the last menstrual period is not known or is unreliable, or the dating scan differs from the last menstrual period dating by more than 5 days. Ultrasound examinations from 12 to 22 weeks are regarded as being within 10 days of accuracy or up to 10 days earlier or 10 days later than the woman's calculated due date. Ultrasounds performed after 22 weeks gestation cannot be used to estimate the due date of the baby because the size no longer reflects the age how accurate is dating ultrasound well.
Even average babies can differ by up to 2 to 3 "weeks of growth". These scans are only used to estimate the due date of your baby if this is all you have to go on. If you have more than one ultrasound during your pregnancy, how accurate is dating ultrasound you 'multiple dates', then the earliest ultrasound estimate should be used, because it will be more accurate. If you have any questions about this, please feel free to how accurate is dating ultrasound to your sonographer or doctor about it.
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This is presuming that the pregnancy is actually at this stage of development. Sometimes a trans-vaginal examination shows that your pregnancy is less advanced than expected. How accurate is the ultrasound examination? The earlier the ultrasound is done, the more accurate it is at estimating the baby's due date. Also the fetus cannot bend and twist too much yet, so the length of the body is fairly constant.
The scan or my dates - which should I believe? As the baby gets bigger, it starts to express its individual growth potential. The size of the baby correlates less and less with its age as time goes on. You can estimate the due date of the baby by using our pregnancy calculator. What can be seen? Pelvic Ultrasound Pregnancy Ultrasound 3D and 4D scanning Prenatal testing Genetic Counselling Glossary of Terms Make a booking Ultrasound Care locations About our doctors About our equipment How accurate is dating ultrasound to bring to your appointment Links and resources Contact Us.
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