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.
The ideal time for a sonographer to assess the gestational age in the first trimester is between 7-10 weeks of pregnancy.
With today's modern equipment, we can obtain very reliable images and measurements of even very early pregnancies, sometimes even seeing a heartbeat as early as 5-6 weeks!
The most common misconception we encounter almost daily, has to do with how accurate ultrasounds are in fixing the EDC at different stages of pregnancy.
Many patients believe that the later in pregnancy an ultrasound is performed, the more reliable the EDC calculated by the ultrasound is.
Perhaps this is because patients reason that since we can see more detail on ultrasound the further along one is (where we can see noses, ears, fingers, the chambers of the heart, etc.) the numbers should be more accurate. Just as children and adults of the same age can vary dramatically in height and weight, when a baby is past the first trimester he/she also can be larger or smaller than average, depending on genetics (how tall the parents are, how much they weighed at birth), nutrition, and coexisting medical conditions (diabetes, high blood pressure, etc.).
One is via the abdomen – transabdominally and the other is through the vagina – transvaginally.