The quality of the equipment and the skill of the sonographer are very important when doing any pregnancy ultrasound.
Generally, ultrasounds which are performed in the first trimester are within 3-5 days of being accurate in terms of assessing gestational age.
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.
With maturity, the size of the baby correlates less to its age than in the early weeks.
There are two ways of having a seven week ultrasound.
But with every day which passes, the embryo becomes bigger and more advanced in its development.
A duration of only a week can make a significant difference in terms of what can and can’t be seen.
They are also not as mobile and active as they will be with future development.
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.
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.
Later on as the pregnancy progresses, a full bladder is not necessary as the enlarging uterus is no longer contained in the pelvic rim.