Miscarriage in early pregnancy is not uncommon. Many medical experts at home and abroad have conducted a lot of research in the hope of finding the cause of early miscarriage. So far, although it cannot be said to be fully understood, the view that “early miscarriage is a natural elimination process” has been generally accepted. Usually the earlier the miscarriage occurs, the more likely it is to be due to chromosomal abnormalities. More than 50% of early miscarriages are due to chromosomal abnormalities in the embryo, and about 35% of mid-term miscarriages are due to chromosomal abnormalities. There is no doubt that such chromosomal abnormalities are of no value in preserving the pregnancy and the chances of successful preservation of the pregnancy are slim. In natural conception, progesterone levels are produced by the ovarian corpus luteum in the first 6 weeks of pregnancy and are low, at 10-20 ng. After 8 weeks of gestation, the progesterone level gradually increases as the placenta, which is capable of producing progesterone, gradually forms. However, in the special case of IUI, as the embryo needs progesterone support, additional progesterone supplementation is usually required and reaches about 40 ng in the early stages. In clinical practice, many mothers-to-be confuse these two situations and ask for repeated monitoring of progesterone levels despite natural conception, which leads to high doses of progesterone supplementation, making doctors laugh and cry. There is also a misunderstanding caused by not reading the dose units of progesterone monitoring. Some of the different kits in clinical use today are in nanograms and some in nanomoles, so it is best to ask your doctor to help you convert to the same units before comparing them. Early miscarriage due to progesterone deficiency is less common There are many causes of early pregnancy miscarriage, including some chronic diseases and uterine abnormalities, in addition to chromosomal abnormalities. Although low progesterone levels are also a cause of early pregnancy miscarriage, they are so rare that William’s Obstetrics, the foremost authority on obstetrics, does not list them among the common causes of early pregnancy miscarriage. It is generally unknown whether the two factors, low progesterone levels and embryonic dysplasia, are the result of a pre-existing progesterone deficiency causing embryonic dysplasia or whether the embryonic dysplasia affects progesterone levels. Therefore, progesterone supplementation during early pregnancy is only indicated for some specific pregnant women, such as those with luteal deficiency and after ovarian surgery in early pregnancy. Special types of progesterone preparations may be recommended for the prevention of preterm labor in patients with a previous history of spontaneous preterm labor and in those with a shortened cervical canal found in mid-pregnancy; for most expectant mothers with spontaneous pregnancies, repeated monitoring and supplementation of progesterone in early pregnancy is not necessary.