My last period was 23 feb, my hCG level went from 28 to 42 is this could be a miscarriage as my hCG level is very low?

Rising BHCG . Bhcg should increase by about 66% every 48 hours. You numbers are very low and it is unclear over what time period the two numbers were done. You will need to continue to follow the levels to see if they rise normally. Once they reach about 1500 a pregnnacy could be detected by sonogram. Good luck.
Family practice . You actually are not 4 weeks pregnant probably 2weeks or less because you ovulate around day 14 of your cycle. So a low level may mean you are early. Get another level in 2 weeks.
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