Overview of low molecular weight heparin for preventative treatment of adverse obstetric outcomes related to abnormal placentation

Serum mannose-binding lectin (MBL) concentrations are reduced in non-pregnant women with previous adverse pregnancy outcomes

Mannose-binding lectin (MBL) is an important component of the innate immunity, and it is responsible not only for opsonization of micro-organisms, but also for efferocytosis. The aim of this study was to investigate whether MBL concentrations and lectin complement pathway activity are altered in non-pregnant women with previous adverse pregnancy outcomes. Patients were divided into four groups on the basis of their history of pregnancy complications, including control patients who had uncomplicated pregnancies and term deliveries (control, n = 33), and three groups of patients with a history of pregnancy complications, including preterm labour (n = 29), recurrent miscarriage (n = 19) or unexplained intrauterine foetal death (IUFD; n = 17). All women enrolled in the study had an interval of three to six months following their previous pregnancy, and they agreed to have a blood sample taken. We found significantly higher MBL concentrations and functional activity of the lectin complement pathway in healthy controls who had previous uneventful term pregnancies (1341 ng/mL; activity 100% (IQR: 62%-100%)), compared to women with the history of IUFD (684 ng/mL, P = .008; activity 8.5% (IQR: 0%-97.8%), P = .011), recurrent miscarriage (524 ng/mL, P = .022; activity 44% (IQR: 4%-83%), P = .011) or preterm labour (799 ng/mL, P = .022; activity 62.5% (IQR: 0%-83%), P = .003). Our results suggest that inadequate function of the complement lectin pathway is associated with a higher risk of preterm labour, recurrent miscarriage and unexplained intrauterine foetal death.

The complement system and adverse pregnancy outcomes

Adverse pregnancy outcomes significantly contribute to morbidity and mortality for mother and child, with lifelong health consequences for both. The innate and adaptive immune system must be regulated to insure survival of the fetal allograft, and the complement system is no exception. An intact complement system optimizes placental development and function and is essential to maintain host defense and fetal survival. Complement regulation is apparent at the placental interface from early pregnancy with some degree of complement activation occurring normally throughout gestation. However, a number of pregnancy complications including early pregnancy loss, fetal growth restriction, hypertensive disorders of pregnancy and preterm birth are associated with excessive or misdirected complement activation, and are more frequent in women with inherited or acquired complement system disorders or complement gene mutations. Clinical studies employing complement biomarkers in plasma and urine implicate dysregulated complement activation in components of each of the adverse pregnancy outcomes. In addition, mechanistic studies in rat and mouse models of adverse pregnancy outcomes address the complement pathways or activation products of importance and allow critical analysis of the pathophysiology. Targeted complement therapeutics are already in use to control adverse pregnancy outcomes in select situations. A clearer understanding of the role of the complement system in both normal pregnancy and complicated or failed pregnancy will allow a rational approach to future therapeutic strategies for manipulating complement with the goal of mitigating adverse pregnancy outcomes, preserving host defense, and improving long term outcomes for both mother and child.