Dating and viability What is a dating scan?
A dating scan is an ultrasound examination which is performed in order to establish the gestational age of the pregnancy. Dating scans also viability and dating scan other important information such as: the number of fetuses and gestation sacs the presence of a heart beat the size of the fetus, from which the gestational age is estimated unusual features of the uterus such as the shape or the presence of fibroids How is it done?
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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 the transvaginal approach will give better pictures. For transvaginal ultrasound you can have an empty bladder When is it recommended?
Dating scans are usually recommended if there is doubt about the validity of the last menstrual period. For example if you do not know when the first day of your last period, or the likely day of viability and dating scan was have had irregular periods have had an unusual cycle because you recently stopped the oral contraceptive pill, or you recently had a miscarriage, or you are breast-feeding had some implantation bleeding which can be been confused with your last period date What can be seen?
An Early Pregnancy Scan (sometimes also called a Viability Scan or Dating Scan ) provides reassurance in this very early stage of your pregnancy. A pregnancy. Ultrasound in early pregnancy (before 12 weeks) – Dating Scan. Ultrasound in early pregnancy. Ultrasound: • Is a scan that uses sound waves to create a.
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.
This is presuming that the pregnancy is actually at this stage of development.
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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. 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. Also the fetus cannot bend and twist too much yet, so the viability and dating scan of the body is fairly constant. However, the accuracy of the ultrasound examination is always dependent on the skill of the sonographer and the quality of the equipment.
The scan or my dates - which should I believe?
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. 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. 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 viability and dating. 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 very 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 scan during your pregnancy, giving 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 talk to your sonographer or doctor about it.
Queensland X-Ray Women's Imaging Radiologist, Dr Kerry McMahon and Brisbane GP, Dr Wendy Burton discuss how soon is it too soon to come for a scan, the best.
You can estimate the due date of the baby by using our pregnancy calculator.