Thus, a simple and accurate way to "date the fetus" in an early pregnancy is to add the length of the fetal pole (in mm) to 6 weeks.
Using this method, a fetal pole measuring 5 mm would have a gestational age of 6 weeks and 5 days.
Transvaginal ultrasound, by contrast, can detect pregnancies earlier, at approximately 4 to 5 weeks gestation.
Prompt diagnosis made possible by transvaginal ultrasound can, therefore, result in earlier treatment.
Transabdominal ultrasound will provide a panoramic view of the abdomen and pelvis and is noninvasive, whereas transvaginal ultrasound provides a more limited pelvic view and requires insertion of a probe into the vagina.
Transabdominal ultrasound cannot reliably diagnose pregnancies that are less than 6 weeks gestation.
While your sonographer takes measurments they will explain what you are looking at.
It may not be easy for you to make out what you are seeing on the screen in the early scans.
First trimester ultrasonic scans may show 'soft' markers for chromosomal abnormalities, such as the absence of fetal nasal bone or an increased fetal nuchal translucency (back of the neck) to enable detection of Down syndrome fetuses.
By the time the embryo becomes visible on ultrasound the sac diameter is no longer accurate in estimating gestational age.
If cardiac activity can be detected but the embryo is not measurable, the GA is about 5.5 to 6.0 weeks.
The embryonic pole appears adjacent to the yolk sac, soon showing cardiac activity.
Since the connecting stalk is short, the embryonic pole is found near the wall.