Clinical Pharmacology of Dexamethasone in Pregnant Women With Preterm Labor

Inclusion Criteria: * Aged 20-40 (inclusive); * Body mass Index (BMI) 18.5-27.9kg /m2 (inclusive) * Single and twin pregnancy; * Premature delivery at 24-36 weeks; * No antibiotics, prebiotics or probiotics were used one month before feces collection (such as Bifidobacterium triplex live powder, Lactobacillus acidophilus tablet, compound Lactobacillus acidophilus tablet, Bacillus subtilis diplex live intestinal capsule, etc.); * Preeclampsia patients accounted for about 1/10 of each group; * Use dexamethasone I.M. 5mg Q12h regimen (or other dexamethasone administration regimen) to promote fetal lung maturation. Exclusion Criteria: * Ectopic pregnancy; * Suffering from diabetes, fetal distress, serious infectious diseases (such as sepsis, septic shock), fever; * Those who have taken glucocorticoid drugs within 2 weeks before joining the clinical trial; * Those who took clindamycin during the study period; * Congenital fetal malformation or fetal hypoxia in early pregnancy; * Convulsive patients; * HIV/HCV/ HEPATITIS A, drug abuse history; * Suffering from chorioamnitis, endometritis; * Placental abruption, severe intrauterine bleeding; * Pregnant women whose cervical dilation is greater than or equal to 4 cm or whose cervical length is less than or equal to 20 mm by ultrasound examination; * Pregnant women who took food or drugs during the study that might affect the safety of the fetus; * Pregnant women participating in other clinical trials.