What is spontaneous preterm birth? Preterm labor is divided into medically induced preterm labor and spontaneous preterm labor. As the name suggests, medically induced preterm labor is caused by a doctor’s decision to terminate a pregnancy before 37 weeks after balancing the maternal and infant advantages and disadvantages of continuing the pregnancy and terminating it. There are many causes of spontaneous preterm labor, such as contractions caused by various reasons alone or in combination, infection, premature rupture of membranes, cervical insufficiency, etc. leading to the birth of a fetus before 37 weeks. 1, the mechanism of action of progesterone It is currently believed that the main mechanism of action of progesterone is to maintain the uterus in a resting and relaxed state, which is conducive to the fertilization of the egg and the maintenance of human pregnancy; progesterone locally in the cervix can inhibit the release of inflammatory factors, thus inhibiting the softening and dilation of the cervix; progesterone also has an important role in maintaining and protecting the cervical mucus plug, which indirectly plays a role in preventing upstream infection to strengthen the cervix. 2. Progestins and prevention of singleton preterm birth The progestins often studied and discussed in various domestic and foreign guidelines include 17α hydroxyprogesterone caproate (referred to as 17P), the recommended use of which is 250mg intramuscular injection/week; vaginal micronized progestin capsules (domestic drugs such as Angiotensin, 100mg/capsule), the recommended use of which is 100-200mg/day placed vaginally; vaginal progestin gel (domestic The recommended use of vaginal progestogen gel (domestic drug such as Xanax, 90mg/capsule) is 90mg/day vaginally. There is probably no hotter topic in the last decade or so than this one. There is a growing consensus on the role of progesterone, but more recently, there has been more discussion about whether progesterone can prevent preterm birth in singleton, low-risk (or “normal”), primiparous women with no history of preterm birth. If we could, we would have found a preventive measure that would allow for routine ultrasound screening of all pregnant women for cervical length. As we all know, one of the main reasons why there is currently no routine screening for cervical length is that there are no good interventions available. Of course, reaching this conclusion will not be as consistent as one might think, and it will be a constant process of evidence-rebuttal-evidence-rebuttal. We are happy to verify and analyze the “unscientific” aspects of various studies with a “scientific attitude”. For example, in the much cited 2003 Meis study, we questioned the 55% preterm birth rate in the placebo control group, which was higher than that reported in many studies. Subsequently, people used different progestin preparations, different doses, and validated them for different populations, with different conclusions for you and me. 3. Progestins and prevention of preterm birth in twin pregnancies Interestingly, several studies did not find progestins useful in twin or multiple pregnancies. This is incomprehensible to many experts. Although the mechanism of occurrence of singleton and twin preterm births may be different, the mechanism of action of progesterone should be useful for the prevention of at least some twin preterm births. For example, progesterone has a resting effect on the uterus, acts locally on the cervix to inhibit cervical softening and dilation, and protects the cervical mucus plug, etc. Why does it discriminate against twins and multiple births? However, at least up to now, no good evidence has been found to support the use of progestins in twin or multiple births to prevent preterm labor. In fact, some doctors still recommend it some of the time. Because TA believes: medicine is progressive! Although there is no evidence at the moment, maybe sometime in the future the evidence will be so available! At least it is not harmful to the patient, and it is still safe. At least TA abides by the first principle of medicine – the principle of do no harm! 4. Oral Progestins and Preterm Birth Prevention Over the past decade, researchers have hypothesized that the occurrence of various complications of pregnancy, such as pre-eclampsia, spontaneous abortion, pre-eclampsia, and preterm birth may originate from cellular immune effectors related. Dydrogesterone (trade name, Daphne), a highly selective progestin, inhibits pro-inflammatory factors and increases anti-inflammatory cytokines, which may be beneficial in preventing preterm labor by regulating the production of pro- and anti-inflammatory cytokines by lymphocytes in the peripheral blood of pregnant women. Some scholars have followed up pregnant women with ultrasound suggestive of subchorionic hemorrhage by giving 40 mg of oral detrofloxacin and found that the rate of miscarriage was reduced. However, there is no strong probative evidence for oral administration and no evidence for which oral progestin can prevent preterm delivery. However, at present, didrogestrel is still widely used in recurrent miscarriage and may have its specific advantages.