The purpose of this study is to evaluate the efficacy of intravenous KW-3357 in patients with early-onset severe preeclampsia by comparing the prolongation days of pregnancy with that of placebo.

Inclusion Criteria:

1. Patients who gave written consent to participate in the clinical trial by their own free will.

2. Patients aged 18 years or older at the time of obtaining informed consent

3. Patients with early-onset PE* 24 weeks 0 days to 31 weeks 6 days of gestation at the time of enrollment

   *: Determine the definition of gestational age based on the ""Guidelines for Obstetrics and Gynecology, Obstetrics, 2020""

4. Patients diagnosed with severe PE*

   *: Follow the diagnostic criteria of the Japan Society for the Study of Hypertension in Pregnancy

5. Patients with AT activity of 100% or less in the preliminary examination

Exclusion Criteria:

1. Patients who are judged to require immediate delivery*

   *""Best Practice Guide 2015 for Care and Treatment of Hypertension in Pregnancy"" Requirements for Considering Pregnancy Termination Regardless of Pregnancy Weeks in Pregnancy-induced Hypertension Syndrome Cases will be consulted for judgment.

2. Patients with right hypochondralgia or epigastralgia

3. Patients with HELLP syndromes

4. Patients with pulmonary edema

5. Patients with severe pleural effusion, severe ascites, or serous retinal detachment

6. Patients with central nervous system disorders (eclampsia, stroke) or visual disorders (cortical blindness)

7. Patients with severe headache or urge eclampsia

8. Patients with abruptio placentae

9. Suspected patients with 8 or more obstetric DIC scores

10. Patients with a definitive diagnosis of congenital AT deficiency

11. Patients with diseases or symptoms other than the primary disease requiring immediate delivery

12. Patients on ongoing treatment with nonsteroidal anti-inflammatory drugs (NSAIDs, e.g., aspirin) or who require NSAIDs use during the course of the study.

13. Patients who have received the following drugs within 72 hours before administration of the investigational product, etc., or who require administration of the following drugs during the study period (from the start of administration of the investigational product, etc., until the date of termination of pregnancy); heparin, low-molecular-weight heparin (e.g., enoxaparin ordalteparin), fondaparinux, antiplatelet drugs (e.g., clopidogrel, prasugrel, aspirin), direct thrombin inhibitors (e.g., dabigatran), or anticoagulants (e.g., AT preparations).

14. Patients with a current or past history of serious drug allergy

15. Patients with a history or complication of drug dependence or alcoholism

16. Patients with hypersensitivity to AT preparations

17. Patients who are pregnant with a fetus with a chromosomal abnormality or a fetus suspected of having a serious malformation syndrome

18. Patients with multiple pregnancies

19. Patients with a history or complication of antiphospholipid antibody syndrome

20. Patients with diabetes complicated pregnancy or obvious diabetes mellitus

21. Patients with uncontrollable or significant complications, including the following

    • Clinically significant cardiovascular diseases, etc. (New York Heart Association cardiac function classifications Class III or higher)
    • Serious hepatic disease
    • Serious renal disease
    • Pneumonia, interstitial lung disease or other severe respiratory disease
    • Blood disorders such as idiopathic thrombocytopenic purpura
    • Psycho-central nervous system disorders that may affect informed consent
    • Endocrine disorders such as hyperthyroidism
    • Autoimmune diseases such as systemic lupus erythematosus

22. Patients with active malignancy or patients with a history of onset or treatment of malignancy within 5 years before pregnancy (excluding excised or surgically cured basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or ductal carcinoma of the breast, and excluding cervical intraepithelial neoplasia regardless of excised or surgically cured or not)

23. Patients with active infections (e.g., toxoplasma infection, genital chlamydia, genital herpes, cytomegalovirus infection)

24. Patients with a positive history for HIV antibody. Patients with a positive history for HBs antigen and HCV antibody and with active infection presenting with hepatitis symptoms.

25. Patients with any of the following laboratory abnormalities in preliminary examinations

    • Patients with AST or ALT 2 times the upper limit of the reference level of the trial site
    • Cr >=1.1 mg/dL

26. Patients who have participated in a clinical trial or equivalent study of a drug or medical device within 4 months before pregnancy (within 6 months for biologics) and have received the investigational drug or used an unapproved medical device

27. Other patients whom the principal investigator or the subinvestigator judges to be unfavorable for participation in the clinical trial

The datasets generated and/or analyzed during the study sponsored by Kyowa Kirin will be available in the Vivli repository, https://vivli.org/ourmember/kyowa-kirin/ as long as conditions of data disclosure specified in the policy section of the Vivli website are satisfied.