Ultrasound for dating 100 perscent dating
However, if you did not get a first trimester ultrasound for dating and an ultrasound done to look at the baby's anatomy (usually at 18-20 weeks of pregnancy) differs from your LMP date by 10 to 14 days, we would change your date to the ultrasound estimate.
At around seven weeks of pregnancy, it’s reasonably common for women to have their first ultrasound.
The ideal time for a sonographer to assess the gestational age in the first trimester is between 7-10 weeks of pregnancy.
This is the period of time which provides the most accurate assessment.
With this form of scan it is not as necessary for the mother to have a full bladder.
When having a transabdominal ultrasound, however, a full bladder is necessary in order to “lift” the uterus up and out of the pelvis so the embryo can be seen more clearly.
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.
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.Later on as the pregnancy progresses, a full bladder is not necessary as the enlarging uterus is no longer contained in the pelvic rim.In very early pregnancy, the embryo and pregnancy sac may simply be too small to see very much at all.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.