Instead of ultrasounds, physicians may choose to monitor pregnancy viability and progression using blood tests for hormones and measurement of uterine size.American notes that it's not unusual for a woman to go through the entirety of a normal, uncomplicated pregnancy without a single ultrasound, if that's the preference of her physician.
Here, notes American Pregnancy.org, transvaginal ultrasound may provide a rough estimate, but can’t necessarily pinpoint the age of the embryo.
The reason for this is that differences in women’s reproductive cycles and differences in embryonic growth rate affect embryo size.
If the pregnancy is very early it may be normal not to clearly see the fetal pole or heart beat.
In this case a follow up scan after an interval when normal growth can be expected to now show these things will be recommended.
Ultrasounds help physicians assess the viability of a pregnancy with regard to placement of the embryo, gestational age, and visible signs of appropriate development.