If i had unprotected sex sept 18, when can i take a beta hcg blood test to check if im pregnant? when will the hcg hormone show up?

About 2 weeks from the time of ovulation. Can check around the time of expected menses.

Conception occurs within day or so of the sex. It takes about 3 weeks for the embryo to make enough HCG for a positive pregnancy test. Blood test may be done a day after a missed period. Home pregnancy tests should be done 4-5 days after the missed period. If the result is negative repeat the test in 4-5 days. Use first morning urine and follow instructions for the test carefully.