Study design: Observational with cohort control group. Methods: Size of study groups(s): The sample size calculated for this study was based upon a repeated analysis of variance measures design with 1 between factor and 1 within factor that has 2 groups with 12 subjects each for a total of 24 subjects. Each subject is measured 4 times. This design achieves 84% power to test a difference between groups if a Geisser-Greenhouse Corrected F Test is used with a 5% significance level and the actual effect standard deviation is 0.50 (an effect size of 0.63), achieves 100% power to test a difference within groups across time if a Geisser-Greenhouse Corrected F Test is used with a 5% significance level and the actual effect standard deviation is 0.50 (an effect size of 1.41), and achieves 100% power to test a group by time difference if a Geisser-Greenhouse Corrected F Test is used with a 5% significance level and the actual effect standard deviation is 0.50 (an effect size of 1.41). Patient entry, exclusion and dropout criteria: All women scheduled for a Cesarean-hysterectomy will be asked to enroll in the study, as well as the women with the following diagnoses, which puts them at increased risk for Cesarean hysterectomy: placenta previa, placenta accreta, vaginal trial of labor after aa previous Cesarean delivery.

Protocol specific methods: Written, informed consent will be obtained from all subjects. A blood sample will be obtained shortly after admission to the hospital. In women who go on to have a hysterectomy (anticipated N = 12), blood samples will be obtained at predefined time periods (at time of decision to perform hysterectomy, with every clinically indicated blood draw for coagulation tests, 2, 8, 24 and 48 h after delivery (approximately 9 coagulation panels per subject = approximately 70 mL per study subject for study tests). The next patient at risk of Cesarean hysterectomy, but who does not go on to have a hysterectomy, will serve as a cohort control. Blood samples will be drawn at 2, 24 and 48 h after delivery for coagulation testing (4 coagulation panels per subject = 50 mL). Baseline samples from all other study subjects will be discarded and no further blood work will be obtained.

Obtaining blood for coagulation tests: Every patient at risk for hemorrhage has at least one peripheral intravenous cannula inserted upon admission to the Labor & Delivery Unit. A 2nd IV cannula is almost always placed, usually when the decision is made to proceed with a Cesarean delivery. All study subjects will have a 2nd IV cannula placed for drawing blood for study coagulation tests, and any other clinically indicated blood tests. The cannula will be connected to a stopcock with a "heparin lock" (cannula and stopcock are flushed with saline between aspirations) and left in place for 48 hours after delivery.

Coagulation tests: Blood for coagulation tests will be withdrawn from the 16 gauge IV cannula-stopcock, after aspirating a 5 mL blank. The blank blood will be returned to the study subject immediately after the sample blood is withdrawn and the catheter-stopcock will be flushed with saline solution. The following coagulation tests will be performed at each time period: 1) complete blood count (CBC) (4 mL), prothrombin time (PT), and activated partial thromboplastin time (aPTT) (4.5 mL): NMH laboratories; 2) fibrinogen, d-dimer, antithrombin, thrombin-antithrombin complex, plasminogen, plasminogen-antiplasminogen complex (2 mL): Dr. David Green's laboratory (NU); and 3) thrombelastography (TEG) (2 mL): Dept. of Anesthesiology. The total amount of blood for each coagulation panel is 12.5 mL. If blood is withdrawn for clinically indicated coagulation tests, an extra 4 mL will be withdrawn for study tests.