Is hCG secreted after implantation?

Patient's question:

No

Doctor's answer:

The fertilized egg must implant before it can secrete HCG, and it takes 8 days from intercourse to implantation. A certain concentration is required. Therefore, it takes about 10 days after implantation to detect it. So, if you got a weak positive on the test on March 28th, you should have been pregnant before the 18th.