The short answer to the question when hCG is produced is that it happens directly after implantation. But unfortunately, that does not mean that you are able to take a pregnancy test immediately after that, at around six to twelve days post-ovulation. Very early on in pregnancy, before a woman has missed her period, pregnancy is more easily determined through a blood test, which can also measure hCG levels. For most of us, waiting a little longer until we can "pee on a stick", as pregnancy tests are referred to on internet forums, is more realistic. The levels of hCG in a woman's body should continue to rise steadily until around the 12th week of pregnancy as calculated with the help of the date of her last menstrual period. It is still important to know that all home pregnancy tests are different, and have various levels of sensitivity to hCG.
In general, all pregnancy tests should turn up an accurate result on the day of a missed period. Low hCG levels can indicate the start of a miscarriage and are reason for concern. Multiple pregnancies, on the other hand, cause a more rapid rise in hCG levels earlier on in pregnancy. Because home pregnancy tests do not give the exact levels of hCG, but just tell you whether or not they are detecting any hCG, a visit to your doctor or midwife to determine your exact levels of this hormone are the safest bet.