In a normal pregnancy, the embryo must settle in the appropriate part of the uterine cavity and continue to grow and develop in the uterine cavity until full term, when labor and delivery occur. A spontaneous abortion occurs if the embryo grows and develops in the uterus for too short a time. Spontaneous abortion occurs in 31% of cases after embryo implantation, 80% of which are early abortions. About 2/3 of early miscarriages are clinically silent miscarriages, i.e. miscarriages that occur before the menstrual period, also known as chemical pregnancy. So, are biochemical pregnancy, failure to conceive and miscarriage the same thing? Here we will revisit and learn about each concept: Implantation: is the process in which the embryonic blastocyst in an activated state interacts with the uterus in a receptive state, eventually leading to the establishment of a close connection between the embryonic trophoblast and the endometrium. Failed implantation: refers to the failure of the embryo to implant due to an abnormality at some point prior to the process of establishing this close association with the endometrium. Biochemical pregnancy: is a pregnancy in which the embryo has begun to implant, the trophoblastic ectoderm has invaded the uterine meconium, and the β-HCG secreted by the embryo enters the maternal bloodstream and reaches detectable levels, except that for some reason the pregnancy does not continue thereafter and the β-HCG in the blood or urine is only transiently elevated; the reason for a biochemical pregnancy is that the pregnancy has only progressed to a stage where it can be detected by biochemical methods and has not developed It can be considered a special type of early pregnancy loss (FTPL). Miscarriage: it is a clinical pregnancy loss that occurs after the embryo has been implanted. Thus, failure of implantation, biochemical pregnancy and miscarriage all fall under the category of embryo or pregnancy loss, but occur at different physiological stages and are not the same thing. The causes of failure to conceive, biochemical pregnancy and miscarriage are also different. Failure of implantation is mainly due to maternal factors, embryonic factors, and abnormalities in the dialogue between the two. Maternal factors include decreased endometrial tolerance (abnormal uterine cavity structure, hydrocele, thin or poorly formed endometrium, abnormal expression of molecules related to endometrial tolerance, etc.), immunological abnormalities, etc.; decreased embryonic implantation ability is mainly caused by embryonic chromosomal abnormalities, aneuploid embryos, poor embryonic environment, etc.; and the dialogue between embryo and endometrium begins to reach immune compatibility and neonatal vascularization, thus completing the implantation process, abnormal dialogue between the two may lead to the occurrence of implantation failure. The mechanism of occurrence of biochemical pregnancy remains unclear and may be related to factors such as embryo, endometrium, immune regulation, and ovulation promotion protocols. According to foreign studies (Dickey’s study suggests a higher chance of biochemical pregnancy with endometrial thickness <22.5 px) it is believed that most biochemical pregnancies may be due to endometrial factors, which may originate from anatomical, immunological or other causes of reduced endometrial tolerance. Miscarriage, on the other hand, is mainly due to genetic defects of the embryo, in addition to endocrine abnormalities, autoimmune factors and infectious factors, while midterm pregnancy loss is mostly due to abnormalities of the reproductive tract, such as cervical relaxation. Biochemical pregnancy has a high incidence in both natural pregnancy and IVF populations. Thankfully, however, most current scholarly studies agree that biochemical pregnancy and miscarriage are positive predictors of the success of subsequent IVF treatment. Therefore, there is no need to worry if a biochemical pregnancy or miscarriage occurs after natural conception, as this is the result of natural elimination and usually does not affect the next conception, but if you experience "biochemical pregnancy" repeatedly, you need to actively look for the cause and treat it symptomatically. The causes, mechanisms and processes of pregnancy and miscarriage are different, so each individual needs to be treated individually and symptomatically in order to remove obstacles to the success of the next IVF treatment.