Low HCG level in 3.5 weeks. Is my HCG really low to worry?

Patient: Hi, My LMP was 11/07/2014 but, i know we started trying for baby only after 11/15/2014. Since doctor is calculating from LMP she says i am 5 weeks pregnant now. I had a beta hcg done on 12/04/14 i.e as per doc i was be 3.5 weeks pregnant and the result was 179.8. I am worried since then as doc says it is quite low for 3.5 weeks pregnancy. Can you please tell me what should be the proper reading for hcg at 3.5 weeks? I am going for a usg on 20th i.e as per doc i will be 6 weeks by then but, i am too worried as my hcg was low and per my calculation i would be only 5 weeks then.

Symptoms: Pregnancy

Doctor: Hello,It is to be understood that gestational age is to be calculated from LMP for all practical purposes unless dat ing scan which would be performed on 20th would show a dating discrepancy or your periods had been irregular and you didn’t have good dates, in those cases USG LMP is taken for calculation.So at 5 weeks your HCG values are really less, but it is possible that you may have had a delayed conception, so the beta hcg levels are in accordance with that. If a beta hcg test is repeated after 48 hrs of the previous test and the levels are double , it indicates a growing pregnancy and possibly a viable pregnancy.Hence , get the usg done and they would be looking for a gestational sac with fetal pole and a possible fetal cardiac activity which should get established by 6 weeks mostly and they may perform a hcg test again to look for raised levels. A 6 week hcg level should be 5000 around.I hope i have answered your query in detail,wishing you good health,regards