Beta hcg and PAPP A

neenu • in 20's pregnant with my 🌈. Waiting for my baby

Im 28 weeks pregnant and my doctor said i have to get a pappa and bhcg at 30 weeks any idea as to why it is asked i thought bhcg was done only in 1st trimester. Has any one had this before and what is papp analysis. I have very bad anxity now because i don't know why it is done some one plese help me