This study is a prospective observational study. The participants including 40 pregnant women who have been filed and delivered in our hospital will enrolled, collect venous blood will be collected at different stages of pregnancy, delivery, postpartum to detect the concentration of fetal free DNA, the frequency of associated immune cells, and the expression of functional molecules, so as to explore the immunological mechanism of delivery initiation.

This study is a prospective observational study. The participants including 40 pregnant women (20 normal parturients and 20 pregnant women with threatened preterm delivery) who have been filed and delivered in our hospital will enrolled, collect venous blood will be collected before 12 weeks of pregnancy, at 24 weeks of pregnancy, at 36 weeks of pregnancy, during parturition, and at 42 days after delivery to conduct the following research: 1) Studying the frequency of peripheral blood MDSCs, pDC and NK cells and the expression of functional molecules at different stages of pregnancy (12,24,36 weeks of pregnancy), before delivery and 42 days after delivery through the expression of relevant functional molecules. 2) Detecting the levels of cytokines and chemokines in peripheral blood at different stages of pregnancy (12,24,36 weeks of pregnancy), before delivery and 42 days after delivery, including: IL-1 β, IL-6, IL-10, IL-18, TGF- β and TNF- α, GM-CSF , IL-23, IL-17, IL-13, IL-4, IL-2, IFN-, IFN-, IL-8, GRO α, GCSF, GMCSM, CCL2, CCL5, CCL26,CXCL8, CXCL12，PGE2, M-CSF, COX2, CCL3, CCL4, CXCL1, IDO, Arg-1, ROS and NO. 3) Detection of cffDNA concentration in peripheral blood at different stages of pregnancy (12,24,36 weeks of pregnancy), before delivery and 42 days after delivery. 4) Detection of frequency of MDSCs, pDC and NK cells and expression of functional molecules in placenta. 5) Frequency of peripheral blood MDSCs, pDC and NK cells, expression of functional molecules, cytokine level and cffDNA concentration in pregnant women with threatened preterm labor. 6) Collecting and studying the demographic data of pregnant women at different stages of pregnancy (12,24,36 weeks of pregnancy), before delivery and 42 days after delivery, adverse events of mothers and infants in the perinatal period, and auxiliary examination data (blood routine test, liver and kidney function, TSH, infection index of Aimei B and C, TSH, blood glucose, blood coagulation function, estrogen and progesterone levels, ultrasound, electrocardiogram, etc).

Inclusion Criteria:

• 20 normal parturients and 20 pregnant women with threatened preterm labor who had undergone antenatal examination and delivery in Beijing Ditan Hospital were fully informed of the risks and volunteered to join the study and signed the informed consent form.

Exclusion Criteria:

• 1. Combined with HCV, HIV, syphilis or other infectious diseases.
• 2. Chronic diseases such as diabetes, hypertension, thyroid disease and autoimmune disease.
• 3. Both husband and wife or their families have delivered congenital abnormal fetus in the past.
• 4. Either spouse is unwilling to participate in this study.

20 normal parturients and 20 pregnant women with threatened preterm labor who had undergone antenatal examination and delivery in Beijing Ditan Hospital were fully informed of the risks and volunteered to join the study and signed the informed consent form.