How soon does the placenta start producing hcg? i got a positive test and believe only 8 days past ovulation. or may i be further along?

Positive test : Home pregnancy tests are very accurate. They are the same tests used in a doctors office. They can detect a pregnancy 7-10 days after conception. The best time to take one is when you miss your period. If you doubt the result you can repeat it in 1-2 days. In your case you may have just detected it early. If your unsure if your last period then you could be further along