A decrease in HCG is usually considered to be fetal arrest, ectopic pregnancy, or physiological; HCG is an indicator that detects conception and usually increases significantly after pregnancy. When the sperm unites with the egg and implants in the uterus, a large amount of HCG is produced to maintain the pregnancy. When the fetus stops developing, this hormone is no longer produced and there is a significant decrease. When the fertilized egg implants outside the uterus, which is not conducive to its growth and development, the hormone produced will also be lower and there is no significant doubling of the value when checked every other day. It is important to pay attention to the fact that an ectopic pregnancy can be serious and life-threatening if it ruptures. It reaches a peak in the tenth week of pregnancy and then decreases naturally, which is physiological and does not require treatment.