Dating scan today
So obtaining accurate measurements and visualising them clearly on the screen is a little easier than when they are able to do somersaults and move around a lot. This is also more likely if you are having a transvaginal ultrasound. One of the reasons for this is because the heart needs to work harder and more efficiently to pump oxygenated blood around its much larger body and brain.The quality of the equipment and the skill of the sonographer are very important when doing any pregnancy ultrasound.
One is via the abdomen – transabdominally and the other is through the vagina – transvaginally.Some sonographers believe that at seven weeks of gestation, transvaginal ultrasound provides the best and most accurate visualisation.This is because the transducer does not need to send sound waves through multiple layers of muscle and tissue to “pick up” the returning images.Other reasons to have a 7 week ultrasound are to: The embryo will be measured from the top of its head, the “crown” to its bottom or “rump”.This is because it is the longest portion of the embryo’s body and provides an ideal measurement baseline of growth and development.The limbs and the yolk sac, though obviously important, are not the primary means of measuring growth.
An average length of the embryo at 7 weeks is anywhere between 5mm-12mm. Obviously, every pregnancy is unique and individual factors influence the size of the embryo at this early stage, and the embryo shows development week by week.
This ten day “window” of days either side of the estimated date of confinement – the, is considered standard practice. Even with the best technology and most proficient sonographers available, ultrasounds do not provide absolute proof of dates, gender, size or the unborn baby’s status.
This applies at whatever stage of gestation the ultrasound is done.
This is why an early pregnancy dating scan, rather than one done in the later stages of pregnancy, is considered more accurate when assessing the expected date of delivery.
With maturity, the size of the baby correlates less to its age than in the early weeks.
This is because although every little embryo is unique, there are still defining characteristics of development which apply to all embryos at particular stages of early gestational development.