Habitual losses associated with the chromosomal factor are due to the abnormal initiation of the embryo and its initial non-viability. Other factors create an unfavorable background for implantation, the formation and normal functioning of the placenta, and the further development of the embryo. As a result of alloimmune disorders, the mother's immune system attacks the "foreign" antigens of the embryo received from the father, the mother's body rejects the fetal egg. Autoimmune reactions lead to damage to maternal tissues, which has an indirect adverse effect on the embryo.
A deficiency or imbalance of sex hormones provokes an inferior gravid transformation of the endometrium, a lack of progesterone leads to impaired immune restructuring. Latent infections potentiate an increase in the activity of local immunity. As a result of thrombophilia (including APS), the balance between the processes of fibrin formation and fibrinolysis during implantation is disturbed, thrombosis of the vascular bed occurs and uteroplacental blood flow is disturbed. All these changes become the causes of inferior trophoblast invasion, impaired placentogenesis and fetoplacental insufficiency.