Additional Study Information: The purpose of this study is to evaluate the safety and effectiveness of ATryn, for the treatment of early onset preeclampsia (high blood pressure during pregnancy). ATryn is is currently approved by the Food and Drug Administration (FDA) and is used to prevent blood clots from forming in patients who are having surgery or giving birth to a child. Eligible women will be randomly assigned to a group that receives either ATryn intravenously everyday until pregnancy or receives a placebo (no active medication) until pregnancy. Screening will consist of a fetal ultrasound, blood draw and urine test as well as a physical examination.