For what's it's worth....the important thing is that the HCG #'s double. Are they doing a 2nd test?
When you say 4wks? Do you mea you're 4wks from LMP? or 4 wks pregnant (6wks from LMP?).
Therefore if you're 4wks from LMP or 2wks from conception HCG should be about 3 to 426. if you are 6 wks from LMP or 4 wks from conception the HCG looks more like 7650 to 229,000. In that case the 42 could be concerning.
Hello-
This website might be helpful to you. I know I'm no expert but it looks like you're fine according to what I read. I'm also thinking that they would've told you it wasn't good when they gave you your number. Try not to worry, although I know it's hard! Good luck.
http://www.americanpregnancy.org/duringpregnancy/hcglevels.html