Week 5 - Gestational Age (Fetal age 3 weeks)
The gestational sac is often the first thing that most transvaginal
ultrasounds can detect at about 5 weeks. This is seen before a recognizable embryo can be seen. Within this week,
at about week 5 ½ to the beginning of the 6th week, a yolk sac can be seen inside the gestational sac. The yolk sac
will be the earliest source of nutrients for the developing fetus.
Human chorionic gonadotropin (hCG) levels can have quite a bit of variance at this point. Anything
from 18 - 7,340 mIU/ml is considered normal at 5 weeks. Once the levels have reached at least 2000, some type of
development is expected to be seen in the uterus using high resolution vaginal ultrasound. If using a
transabdominal ultrasound, some type of development should be seen when the hCG level has reached 3600 mIU/ml.
Although development may be seen earlier, these levels provide a guide of when something is expected to be
Progesterone levels also can have quite a variance at this stage of pregnancy.
They can range from 9-47ng/ml in the first trimester, with an average of 12-20ng/ml in the first 5-6 weeks of
With both hCG levels and progesterone levels, it is not the single value that can predict a
healthy pregnancy outcome. It is more important to evaluate two different values to see if the numbers are
increasing. Levels of hCG should be increasing by at least 60 % every 2-3 days, but ideally doubling every 48-72
hours. Progesterone levels rise much differently than hCG levels, with an average of 1-3ng/ml every couple days
until they reach their peak for that trimester. In situations when there is a concern of an ectopic pregnancy or
miscarriage, hCG levels will often start out normal, but will not show a significant increase or will stop rising
all together, and progesterone levels will be low from the beginning.