See related article, pp 864–872 The remodelling of uteroplacental arteries is a key process in the first half of human pregnancy. The transformation from low-flow/high-resistance to high-flow/low-resistance arteries that ensures sufficient blood supply to meet the requirements of the fetus is caused by a loss of elasticity and vasomotor control. This remodelling is facilitated by perivascular invasion of extravillous trophoblast cells and infiltration of vessel walls by endovascular trophoblast cells. Impaired trophoblast invasion of the myometrial segments is therefore associated with placental hypoperfusion and may play a role in the pathogenesis of some cases of intrauterine growth restriction and preeclampsia. Preeclampsia is a multisystem disorder of pregnancy triggered by placental ischemia and release of placental factors causing widespread endothelial dysfunction.1 The reasons for altered trophoblast invasion in preeclampsia are incompletely understood, but similarities between development of normal placenta and development of cancer point toward a key role of growth factors in normal and abnormal placentation.2 MicroRNAs (miRNA) are becoming increasingly recognized as critical regulators of cellular function. These short noncoding RNA species act via repression of gene targets mediated through binding to miRNA seed sequences usually, but not exclusively, located in the 3′-untranslated region. This interaction leads to a block in translation of the gene to protein or induction of messenger RNA degradation. As such, the expression pattern and potential dysregulation of individual miRNA species, or miRNA signatures in individual cells, tissues, and organs are critical in understanding the role of miRNAs in health and disease. Although the discovery of miRNA was initially made in 1993,3 it is only in recent years that full recognition of their broad importance in cellular homeostasis, as well as the potential of miRNAs as therapeutic entities and as biomarkers of disease has been established. In contrast to diseases such as those …