Recent advances have shown that certain proteins may be present in a pregnant woman's blood very early in pregnancy which can predict who is at the highest risk for developing preeclampsia. These proteins can be measured and may be used to predict a woman's risk of developing preeclampsia.

Special placental cells called endovascular cytotrophoblasts are needed in the early formation of the placenta. These placental cells invade the maternal blood vessels in the formation of the maternal-placental blood interface. HLA-G is a protein produced by the placental cells and prevents these special cells from being rejected by the mother's immune system. Recent studies have indicated that the level of HLA-G is decreased in placentas from mothers with preeclampsia. Progesterone, a naturally occurring hormone produced in pregnancy, has been shown to increase the production of HLA-G in the placental cytotrophoblast cells.

In regards to the treatment of preeclampsia, studies have shown that low dose aspirin if given to mothers who have had severe early preeclampsia, lowers the risk for having preeclampsia again. This study aims to show that low dose aspirin combined with progesterone will decrease the risk of preeclampsia in pregnant women with a history of preeclampsia in a previous pregnancy. Data generated will determine levels and ratios of blood proteins that are predictive of preeclampsia at specific gestational ages.