<qa>  What is the reason for this study?This study is designed to investigate why multiparous women might still be susceptible to rubella. All pregnant women are checked for rubella immunity, and if they are non-immune, there are standard orders in our hospital to administer the rubella vaccine on the post-partum floor prior to discharge home from the hospital. Despite this, some multiparous women are found to be susceptible non-immune, and this study will explore the reasons for this. 