Pre-eclampsia: is it all in the placenta?

Hypertensive disorders of pregnancy complicate almost 7 - 10 % of all pregnancies. The dyad of hypertension and proteinuria after 20 weeks of gestation is referred to as pre-eclampsia. It is a major cause of maternal morbidity and mortality and is also associated with increased perinatal problems. Despite intensive research over the years the exact cause of pre-eclampsia remains unknown. Nevertheless, information gleaned from published studies point to the placenta as the probable pathogenetic focus of pre-eclampsia, as the disease usually resolves within 24 - 48 hours after delivery of the placenta. Although the precise involvement of the placenta in pre-eclampsia remains unclear there are indications that the trophoblastic invasion of the uterine spiral arteries is abnormal in women who develop pre-eclampsia. This impaired invasion leads to decreased placental perfusion and ultimately to placental hypoxia. The distressed or ischaemic placenta then secretes a factor(s) into the maternal circulation, which cause/s widespread endothelial cell dysfunction characterized by vasospasm, activation of coagulation system and organ ischaemia. The cause of the defective cytotrophoblastic invasion of the spiral arteries and the link between placental ischaemia and generalized maternal endothelial dysfunction remain unknown. Although the placenta appears to have a major role in the pathogenesis of pre-eclampsia, evidence also suggests that factors like maternal genetic predisposition, dietary, environmental and behaviour, which surface during the stress of pregnancy might also be involved in the development of pre-eclampsia. It is known that not all women with poor cytotrophoblast invasion develop pre-eclampsia and not all women with preeclampsia show poor cytotrophoblast invasion. Over the years, a number of potential risk factors associated with the development of pre-eclampsia are being recognized and it might be appropriate now to develop some preventative strategies based upon the available information.