I got a positive pregnancy test saturday. monday my hcg was 152 and yesterday it went down to 143. is it possible to have such a slight decrease and have a healthy pregnancy?

Possible: It is possible to have a slight decrease in HCG in early pregnancy but not likely. Sorry I can't give you better news.

Unlikely: The hCG levels typically rise throughout pregnancy until about 12 to 14 weeks when the levels decrease slowly for a few weeks. In early pregnancy, when the levels fall as you describe, it is a sign of a failed pregnancy and there is very little chance for a successful pregnancy outcome. You should be prepared for a miscarriage. See your doctor and keep your followup appointments.