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.Some sonographers believe that at seven weeks of gestation, transvaginal ultrasound provides the best and most accurate visualisation.
However, general “mass” structures such as a head and body can generally be seen in the embryo at seven weeks.
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.
Later on as the pregnancy progresses, a full bladder is not necessary as the enlarging uterus is no longer contained in the pelvic rim.
Like every other health professional, individual skill, expertise and training make a big difference to the outcome of their assessments.
When you are first referred for a seven week ultrasound, the first of many types of ultrasound, ask your GP or maternity care provider who has the best reputation for quality scan results.