Maternal immunity undergoes subtle adjustment in order to tolerate the 
semi-allogeneic embryo and maintain the host defense against potential 
pathogens. Concomitantly, coagulation systems change from an anti-coagulant 
state to a pro-coagulant state to meet the hemostatic challenge of placentation 
and delivery. Innate immunity and blood coagulation systems are the first line 
of defense to protect a host against exogenous challenges, including 
alloantigens and mechanical insults, and preserve the integrity of an organism. 
The interactions between coagulation and immune systems have been extensively 
studied. Immune cells play a pivotal role in the initiation of the coagulation 
cascade, whereas coagulation proteases display substantial immuno-modulatory 
effects. Upon exogenous challenges, the immune and coagulation systems are 
capable of potentiating each other leading to a vicious cycle. Natural killer 
(NK) cells, macrophages (Mphis) and dendritic cells (DCs) are three major innate 
immune cells that have been demonstrated to play essential roles in early 
pregnancy. However, immune maladaptation and hemostatic imbalance have been 
suggested to be responsible for adverse pregnant outcomes, such as preeclampsia 
(PE), miscarriage, recurrent spontaneous abortion (RSA) and intrauterine growth 
restriction (IUGR). In this review, we will summarize the mutual regulation 
between blood coagulation and innate immune systems as well as their roles in 
the maintenance of normal pregnancy and in the pathogenesis of adverse pregnancy 
outcomes.