Originally Posted by
atomic sagebrush
It is how much HCG happened to be in your system when you conceived. Women can have anything from 0-5 HCG and then this doubles so one pregnancy can start off at 0 and then go like this:
0
1
2
4
8
16
and then another could start off at 5 and progress like this:
5
10
20
40
80
160
Two pregnancies (even in the same woman) could have as much as 10x different HCG levels on the same day of the development. So it's entirely possible for one normally developing pregnancy to have much higher HCG levels even if they implanted the same day.