Why did hcg drop and rise after laparoscopic surgery for ectopic pregnancy, why?

After laparoscopic surgery for ectopic pregnancy, human chorionic gonadotropin HCG drops and rises again, a situation where a persistent ectopic pregnancy may have occurred.
Ectopic pregnancy is usually called ectopic pregnancy, refers to the fertilized egg in the uterus outside the body cavity of the bed. Ectopic pregnancy is usually treated with medication, conservative surgery or radical surgery, depending on the individual.
After conservative surgical treatment, the remaining trophoblast cells may continue to grow and bleeding may occur again, causing abdominal pain, a condition known as persistent ectopic pregnancy. If HCG does not fall or rise after surgery, or if HCG does not fall to less than 50% of its preoperative level one day after surgery, it is considered that the pregnancy may be a persistent ectopic pregnancy.