Since October 2009, H1N1 influenza vaccine has developed and approved of immunization in population in China. However, there was little epidemiological evidence of safety when vaccinated in healthy pregnant women. The main objective of this study is to assess the safety of split-virion inactivated H1N1 vaccine without adjuvant when administered in healthy pregnant women. It is a stratified and controlled clinical trial in healthy pregnant women. And participants were included up to 226 healthy pregnant women aged 18 -35 years old who have no history of novel influenza H1N1 infection or novel influenza H1N1 vaccination. The pregnancy week ranged from 5 weeks to 32 weeks. Subjects were divided into 2 groups: vaccinated group（122） and unvaccinated group（104）. Subjects in the vaccinated group were administered one dose of 15μg H1N1 vaccine. Subjects in the unvaccinated group received no vaccine as controls. Safety will be measured by assessment of pregnancy outcomes. And observation time for pregnancy outcomes was lasting for 28 days postpartum since vaccinated; and protective effect was observed for six months.

Inclusion Criteria:

1. Healthy pregnant women
2. Be able to show legal identity card for the sake of recruitment
3. Be able to understand and sign the informed consent

Exclusion Criteria:

1. Cases, cured cases and close contact of influenza A (H1N1) virus
2. Subject that has a medical history of any of the following: allergic history, or allergic to any ingredient of vaccine, such as egg, egg protein, etc
3. Serious adverse reactions to vaccines such as anaphylaxis, hives, respiratory difficulty, angioedema, or abdominal pain
4. Autoimmune disease or immunodeficiency
5. Asthma that is unstable or required emergent care, hospitalization or intubation during the past two years or that required the use of oral or intravenous corticosteroids
6. Diabetes mellitus (type I or II), with the exception of gestational diabetes
7. History of thyroidectomy or thyroid disease that required medication within the past 12 months
8. Serious angioedema episodes within the previous 3 years or requiring medication in the previous two years
9. Bleeding disorder diagnosed by a doctor (e.g. factor deficiency, coagulopathy, or platelet disorder requiring special precautions) or significant bruising or bleeding difficulties with IM injections or blood draws
10. Any history of immunosuppressive medications or cytotoxic medications or inhaled corticosteroids within the past six months (with the exception of corticosteroid nasal spray for allergic rhinitis or topical corticosteroids for an acute uncomplicated dermatitis)
11. History of any blood products or seasonal influenza vaccine administration within 3 months before the dosing
12. Administration of any other investigational research agents within 30 days before the dosing
13. Administration of any live attenuated vaccine within 30 days before the dosing
14. Administration of subunit or inactivated vaccines, e.g., pneumococcal vaccine, or allergy treatment with antigen injections, within 14 days before the dosing
15. Axillary temperature > 37.0 centigrade at the time of dosing
16. Psychiatric condition that precludes compliance with the protocol
17. Any medical, psychiatric, social condition, occupational reason or other responsibility that, in the judgment of the investigator, is a contraindication to protocol participation or impairs a volunteer's ability to give informed consent