Hi, I Went Through IVF And Had A 5 Day

Hi, I went through IVF and had a 5 day frozen blastocyst transfer on the 29th of Feb. I did my first blood test today 9 March and was told my hcg levels are 12mlU/ml, a low positive and asked to repeat a blood test in 2 days time. When I was not pregnant my hcg levels were 2mlU/ml. Do I have anything to worry about with these numbers? My Fertility specialist, when doing the transfer was very skeptical that this one would even take because after the thaw, the blastocyst expanded and then collapse and it had not re-expanded when the transfer was done.