What is a dating and viability ultrasound
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.
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.
Like every other health professional, individual skill, expertise and training make a big difference to the outcome of their assessments.
The ideal time for a sonographer to assess the gestational age in the first trimester is between 7-10 weeks of pregnancy.A duration of only a week can make a significant difference in terms of what can and can’t be seen.At seven weeks of gestation it is still too early to identify what gender (sex) the baby will be.There are two ways of having a seven week ultrasound.One is via the abdomen – transabdominally and the other is through the vagina – transvaginally.
In some respects the seven week ultrasound can be quite accurate because the embryo is developing very quickly.