A drop in HCG at 9 weeks of pregnancy does not necessarily mean that the fetus has stopped, and it is not possible to determine fetal arrest based on a single value alone.
The drop in HCG in 9 weeks of pregnancy may be a slight decrease in HCG values after they reach their peak growth during pregnancy, which is generally normal and cannot be diagnosed as fetal arrest.
To find out whether the fetus has stopped developing in the uterus at 9 weeks of pregnancy, it is recommended to go to the hospital for an ultrasound to check that the fetal heartbeat is good, indicating that the uterus is a live fetus and that there has been no fetal eclampsia. To check that there is no longer a fetal heartbeat in the uterus and the HCG has dropped to consider that it is a fetal arrest.
HCG measurement may be inaccurate or may fluctuate greatly from day to day. Occasional drop in HCG does not mean anything and should be considered in conjunction with other tests.
If the diagnosis of fetal failure is confirmed by ultrasound and the pregnancy cannot continue, you should consult a doctor promptly.