Biochemistry usually occurs within 5 weeks of pregnancy and is also determined in conjunction with blood HCG. A biochemical pregnancy is a miscarriage that occurs before menstruation and is caused by a failure of the fertilized egg to attach, manifested only by vaginal bleeding similar to menstruation and a transient increase in blood HCG (human chorionic gonadotropin) levels, which will drop to normal soon after the vaginal bleeding ends. It usually occurs within 5 weeks of pregnancy and is also known as a clandestine abortion. An occasional biochemical pregnancy does not affect the ability to conceive again, and the pregnancy can be resumed after the vaginal bleeding has ended. However, in the case of recurrent biochemical pregnancy, endocrine examination, immune function examination and chromosome examination of both husband and wife should be conducted under the guidance of doctor to find out the cause, and then prepare for pregnancy again after active treatment.