We know that in order to get pregnant, sperm and egg must meet and unite to form an embryo, and while the embryo is developing, the endometrium is actively preparing for the arrival of the embryo; when the embryo and the endometrium are developing at the same pace, the blastocyst and the endometrium, which is in a receptive state, come into further intimate contact, and eventually the blastocyst burrows into the endometrial layer, and the embryonic trophoblast establishes a close connection with the endometrium. If there is an abnormality at some point before this connection is established, the embryo will not be able to implant and, of course, pregnancy will not be possible. The clinical interpretation of “biochemical pregnancy” may have three meanings: 1. Biochemical pregnancy is an early stage of normal pregnancy; “biochemical pregnancy” means that the embryo has already been implanted and the β-HCG secreted by the embryonic trophoblast has entered the maternal bloodstream and reached detectable levels. This is because the pregnancy has only progressed to a stage where it can only be detected by biochemical methods and has not yet progressed to a stage where the gestational sac can be detected by ultrasound. If the pregnancy continues to the stage where the gestational sac can be detected in the uterine cavity by ultrasound, it is called “clinical pregnancy”. If a clinical pregnancy is followed by a pregnancy loss before 28 weeks of gestation, we call it a “miscarriage”. Therefore, a biochemical pregnancy can only refer to the early stages of pregnancy, where the outcome of the embryo is not known. A biochemical pregnancy can also refer to a pregnancy in which the embryo has implanted, but then for some reason the embryo fails to continue to grow healthily and withers away, and the beta-HCG in the blood drops. The incidence of pregnancy loss after implantation is about 31%, while the incidence of miscarriage after clinical pregnancy is about 15%. The mechanism of occurrence of biochemical pregnancy is still unclear and the influencing factors may be multifaceted and may be related to the developmental potential of the embryo itself, the tolerability of the endometrium, the hypercoagulable state of maternal blood, and the immune dysregulation at the placental interface. Pregnancy loss occurs early, before the formation of the intrauterine gestational sac is detected by ultrasound, and the pregnancy is terminated, which we used to call “early embryonic blight” and “early pregnancy miscarriage”. 3. possible ectopic pregnancy (ectopic pregnancy) miscarriage The reason why we hesitate to define biochemical pregnancy as miscarriage in medical terminology is that there is another possibility. The embryo lays outside the endometrial cavity, such as the fallopian tubes, cervix, ovaries, etc., and cannot continue to develop and dies naturally. Because we do not find a gestational sac in the uterine cavity, how can we prove where the embryo has laid down in such an early pregnancy, when scraping often does not prove an intrauterine pregnancy either? You cannot deny and disprove this speculation of a potential ectopic pregnancy. A “biochemical pregnancy” means that your little angel has been here before, but only for a short time and then left quietly. If a single biochemical pregnancy or miscarriage is fortuitous, you can continue to try to conceive; if multiple biochemical pregnancies occur, especially for those who get pregnant after IVF treatment, you need to seek help from your doctor to find the cause. Therefore, both biochemical pregnancy and miscarriage fall under the category of embryo or pregnancy loss, but occur at different physiological stages and are not the same thing. However, at this time, we cannot define a biochemical pregnancy as a history of a single miscarriage based on rigorous industry diagnostic criteria.