Preterm labor refers to all deliveries before 37 weeks. Very early preterm labor (<28 weeks), about 0.25% of pregnancies Early preterm labor (28-30 weeks), about 0.25% of pregnancies Midterm preterm labor (31-33 weeks), about 0.6% of pregnancies Late preterm labor (34-36 weeks), about 3.0% of pregnancies Types of preterm labor: 1. One-third of preterm births are of medical origin, mainly including hyperemesis and fetal growth restriction. 2. Spontaneous preterm birth: Two-thirds of preterm births are spontaneous, including early onset of labor or premature rupture of membranes. The risk of fetal/neonatal death and mental retardation is significantly higher in patients with very early preterm, early preterm, and midterm preterm births, and the incidence of spontaneous preterm birth before 34 weeks is approximately 1%. Screening for preterm birth: two approaches to identify those at high risk of preterm birth: 1. cervicovaginal fetal fibronectin The cervicovaginal secretions of pregnant women between 22 and 34 weeks show low levels of fetal fibronectin. 25% of pregnant women who test positive for fetal fibronectin between 22 and 24 weeks have spontaneous preterm birth before 34 weeks. 2. cervical length The risk of preterm birth increases exponentially when the cervical length is less than 15 mm between 22 and 24 weeks of gestation. The risk of preterm delivery is exponentially higher. Spontaneous preterm labor occurs before 34 weeks in 30% of pregnancies with cervical length less than or equal to 15 mm. The risk of spontaneous preterm delivery in twin and triplet pregnancies was also associated with cervical length. Combined screening with "cervical length and obstetric history" is a very effective method to predict preterm birth. Prevention of preterm labor: For the prevention of preterm labor in pregnant women with a history of preterm labor, studies have found that the following methods do not reduce the risk of recurrence of preterm labor: 1. Bed rest Bed rest at home or in the hospital is widely used, but there is no scientific evidence. In fact, randomized studies of twin pregnancies have shown that bed rest increases the risk of preterm birth instead. In addition, bed rest has other side effects on pregnant women, including an increased risk of venous thrombosis, muscle atrophy, and putting pregnant women in a state of stress. Prophylactic use of contraction inhibitors and lifestyle interventions include reduced physical effort, increased prenatal visits, psychological support, and dietary supplementation with iron, folic acid, calcium, zinc, magnesium, vitamins, or fish oil. Two methods have been shown to be effective in reducing the risk of recurrent preterm labor: 1. Cervical cerclage Cervical cerclage can reduce the risk of preterm labor before 34 weeks by 25%. There are two clinical management methods for pregnant women with a previous history of preterm labor. First, cervical cerclage is performed in all such pregnancies after screening at 11-13 weeks of gestation has largely ruled out serious fetal anomalies. Second, the cervical length is measured every two weeks and cervical cerclage is performed when the cervical length is less than 25 mm. The overall preterm birth rate is similar after both preventive measures, but the second method is more recommended because it reduces the risk of cervical cerclage by 50% 2. Progesterone The use of progesterone between 20 - 34 weeks reduces the risk of preterm birth before 34 weeks by 25%. Natural progesterone vaginal suppositories can be used, or synthetic 17-alpha-hydroxyprogesterone can be given intramuscularly. Natural progesterone is recommended for one reason: it has fewer side effects (drowsiness, fatigue, headache, etc.); and two: 17-alpha-hydroxyprogesterone may increase the risk of fetal death. Therefore, treating pregnant women with a history of preterm labor: bed rest and prophylactic use of contraction inhibitors (e.g., Ambro) or interventions in normal lifestyle are ineffective, and if a high risk of preterm labor is screened in early pregnancy, the use of natural progesterone vaginal suppositories is recommended to reduce preterm labor by 25%. Cervical length measurement every 2 weeks during 14 - 24 weeks of gestation and prompt cervical cerclage can reduce preterm birth by 25%. Prophylactic use of progesterone or cervical cerclage in singleton pregnancies with a history of preterm labor reduces the chance of recurrent preterm labor by approximately 25%. In singleton pregnancies without a history of preterm delivery, progesterone use reduces the risk of preterm delivery by approximately 45% in women with a high risk of delivery before 34 weeks if a routine vaginal ultrasound scan at 22-24 weeks of gestation reveals a shortened cervix (15 mm or less). For twin pregnancies, the incidence of spontaneous preterm delivery before 34 weeks was 13% compared to 1% for singleton pregnancies. Bed rest in twin pregnancies significantly increased rather than decreased the incidence of early preterm delivery, and cervical cerclage in twin pregnancies with a cervical length of less than 25 mm doubled the incidence of early preterm delivery, and prophylactic progesterone did not reduce the risk of early preterm delivery.