Page 4 - Fetalage Conception Guidline
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 seen.
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 pregnancy.
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.
Week 6 - Gestational Age (Fetal age 4 weeks)
5 ½ to 6 ½ weeks is usually a very good time to detect either a fetal pole or even a fetal heart beat by vaginal ultrasound. The fetal pole is the first visible sign of a developing embryo. This pole structure actually has some curve to it with the embryo’s head at one end and what looks like a tail at the other end. The fetal pole now allows for crown to rump measurements (CRL) to be taken, so that pregnancy dating can be a bit more accurate. The fetal pole may be seen at a crown-rump length (CRL) of 2-4mm, and the heartbeat may be seen as a regular flutter when the CRL has reached 5mm.
If a vaginal ultrasound is done and no fetal pole or cardiac activity is seen, another ultrasound scan should be done in 3-7 days. Due to the fact that pregnancy dating can be wrong, it would be much too early at this point to make a clear diagnosis on the outcome of the pregnancy.
Week 7 - Gestational Age (Fetal Age 5 weeks)