1. Prothrombin time (PT):

PT refers to the time required for the conversion of prothrombin into thrombin, leading to plasma coagulation, reflecting the coagulation function of the extrinsic coagulation pathway. PT is mainly determined by the levels of coagulation factors I, II, V, VII, and X synthesized by the liver. The key coagulation factor in the extrinsic coagulation pathway is factor VII, which forms FVIIa-TF complex with tissue factor (TF). , which initiates the extrinsic coagulation process. The PT of normal pregnant women is shorter than that of non-pregnant women. When factors X, V, II or I decrease, PT can be prolonged. PT is not sensitive to the lack of a single coagulation factor. PT is significantly prolonged when the concentration of prothrombin drops below 20% of the normal level and factors V, VII, and X fall below 35% of the normal level. PT was significantly prolonged without causing abnormal bleeding. Shortened prothrombin time during pregnancy is seen in thromboembolic disease and hypercoagulable states. If PT is 3 s longer than normal control, the diagnosis of DIC should be considered.

2. Thrombin time:

Thrombin time is the time for the conversion of fibrinogen to fibrin, which can reflect the quality and quantity of fibrinogen in the blood. Thrombin time is shortened in normal pregnant women compared with non-pregnant women. There were no significant changes in thrombin time throughout pregnancy. Thrombin time is also a sensitive parameter for fibrin degradation products and changes in the fibrinolytic system. Although the thrombin time is shortened during pregnancy, the changes between different pregnancy periods are not significant, which also shows that the activation of the fibrinolytic system in normal pregnancy is enhanced. , to balance and enhance coagulation function. Wang Li et al[6] conducted a comparative study between normal pregnant women and non-pregnant women. The thrombin time test results of the late pregnant women group were significantly shorter than those of the control group and the early and middle pregnancy groups, indicating that the thrombin time index in the late pregnancy group was higher than that of PT and activated partial thromboplastin. Time (activated partial thromboplastin time, APTT) is more sensitive.

3. APTT:

Activated partial thromboplastin time is mainly used to detect changes in coagulation function of the intrinsic coagulation pathway. Under physiological conditions, the main coagulation factors involved in the intrinsic coagulation pathway are XI, XII, VIII and VI, of which coagulation factor XII is an important factor in this pathway. XI and XII, prokallikrein and high molecular weight excitogen jointly participate in the contact phase of coagulation. After the activation of the contact phase, XI and XII are activated successively, thereby starting the endogenous coagulation pathway. Literature reports show that compared with non-pregnant women, the activated partial thromboplastin time in normal pregnancy is shortened throughout the pregnancy, and the second and third trimesters are significantly shorter than those in the early stage. Although in normal pregnancy, coagulation factors XII, VIII, X, and XI increase correspondingly with the increase of gestational weeks throughout pregnancy, because coagulation factor XI may not change in the second and third trimesters of pregnancy, the entire endogenous coagulation function In the middle and late pregnancy, the changes were not obvious.

4. Fibrinogen (Fg):

As a glycoprotein, it forms peptide A and peptide B under thrombin hydrolysis, and finally forms insoluble fibrin to stop bleeding. Fg plays an important role in the process of platelet aggregation. When platelets are activated, fibrinogen receptor GP Ib/IIIa is formed on the membrane, and platelet aggregates are formed through the connection of Fg, and finally thrombus is formed. In addition, as an acute reactive protein, the increase in plasma concentration of Fg indicates that there is an inflammatory reaction in blood vessels, which can affect blood rheology and is the main determinant of plasma viscosity. It directly participates in coagulation and enhances platelet aggregation. When preeclampsia occurs, Fg levels increase significantly, and when the body's coagulation function is decompensated, Fg levels eventually decline. A large number of retrospective studies have shown that the Fg level at the time of entering the delivery room is the most meaningful indicator for predicting the occurrence of postpartum hemorrhage. The positive predictive value is 100% [7]. In the third trimester, plasma Fg is generally 3 to 6 g/L. During activation of coagulation, higher plasma Fg prevents clinical hypofibrinemia. Only when plasma Fg>1.5 g/L can ensure normal coagulation function, when plasma Fg<1.5 g/L, and in severe cases Fg<1 g/L, attention should be paid to the risk of DIC, and dynamic review should be carried out. Focusing on the bidirectional changes of Fg, the content of Fg is related to the activity of thrombin and plays an important role in the process of platelet aggregation. In cases with elevated Fg, attention should be paid to the examination of hypercoagulability-related indicators and autoimmune antibodies [8]. Gao Xiaoli and Niu Xiumin[9] compared the plasma Fg content of pregnant women with gestational diabetes mellitus and normal pregnant women, and found that the content of Fg was positively correlated with thrombin activity. There is a tendency to thrombosis.