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.At around seven weeks of pregnancy, it’s reasonably common for women to have their first ultrasound.
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.
It is also impossible to do a thorough foetal screening assessment because it is still just too premature in terms of embryonic development.
However, general “mass” structures such as a head and body can generally be seen in the embryo at seven weeks.
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.
With maturity, the size of the baby correlates less to its age than in the early weeks.
In some respects the seven week ultrasound can be quite accurate because the embryo is developing very quickly.
They are also not as mobile and active as they will be with future development.
There are two ways of having a seven week ultrasound.
One is via the abdomen – transabdominally and the other is through the vagina – transvaginally.
This is the period of time which provides the most accurate assessment.