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Pregnancy sometimes can end in sorrow. Miscarriage means the termination of pregnancy before the fetus becomes viable. Based on the gestational age, it refers to cases where the pregnancy ends before the 20th week of pregnancy after the first day of the last menstrual period, or when the fetus weighs less than 500g. Miscarriages are broadly classified into spontaneous miscarriage and medical abortion. Spontaneous miscarriage refers to miscarriage that occurs naturally, while medical abortion refers to miscarriages that are artificially induced using drugs or devices for therapeutic or other purposes. For reference, if the baby dies in the womb and is born after 20 weeks of pregnancy, it is called a stillbirth rather than a miscarriage.
Pregnancy failure refers to the failure to conceive, while miscarriage refers to the failure to continue the pregnancy after it has occurred. This distinction is not easy to make in practical medicine. Because ovulation, fertilization, implantation, and maintenance of pregnancy occur as a continuous series of events, the distinction between each stage is not clear.
Commonly, pregnancy is considered when you have missed your expected period, have a positive pregnancy test in your urine or blood, or sometimes have an ultrasound confirming the pregnancy. However, this also falls under maintaining a pregnancy after fertilization and implantation. Therefore, if we assume that pregnancy begins at the time of conception, the question arises: how should we view the failure or interruption of a pregnancy that occurs before we are aware of it, or that is, between ovulation and the expected date of the next menstrual period? In some circles, this is called a chemical pregnancy, but it cannot be considered a miscarriage as it occurred before pregnancy was clinically confirmed. These types of cases are not clearly defined.
A similar example is frequently observed after in vitro fertilization(IVF), where a healthy embryo(a mass of cells that develop through cell division after fertilization and are in the pre-fetal stage) is transferred but there is no confirmed pregnancy. This is called “implantation failure”. In other words, if fertilization has occurred, there is a similarity to a miscarriage because even if the embryo(s) failed to implant or make it to the early stage of maintaining a pregnancy, it occurred after fertilization aka when the pregnancy was “established”. Along these lines, several recent studies have noted similarities in causes between miscarriage and implantation failure. The miscarriage rate between 5 and 20 weeks of pregnancy is known to be around 10-20%. The earlier the week, the higher the miscarriage rate.
There are cases where the pregnancy test result may be positive but abnormal, which typically include ectopic pregnancy and molar pregnancy. Ectopic pregnancy occurs when a fertilized egg implants in a location other than the uterine cavity, with tubal pregnancy being the most common. Molar pregnancy is a gestational trophoblastic disease, in which the chorionic villi undergo vesicular degeneration for some reason, forming small cysts. Complete moles can progress to malignant choriocarcinoma in 15-20% of cases, and partial moles in 1-5% of cases. All of these cases require drug or surgical treatment.