Placental pathology in early-onset and late-onset fetal growth restriction.

Several histopathological features are found more frequently in placentas from pregnancies complicated by fetal growth restriction (FGR), including villous infarction, maternal vascular changes and villous morphological alterations, although around one quarter of placentas associated with FGR lack any morphological abnormality on routine examination. Since similar changes may also affect clinically uncomplicated pregnancies, the positive predictive value of such findings for pathological FGR in an unselected case remains low. However, the pattern of placental pathologies varies with clinical subgroup. The combination of placental bed and parenchymal lesions in FGR with abnormal uterine artery Doppler velocimetry is essentially identical to preterm pre-eclampsia (PET), and there is an association between FGR with abnormal umbilical artery Doppler findings and lesions of fetal stem arteries and terminal villous hypovascularity. Conversely, placentas from pregnancies complicated by PET or FGR presenting at or near term have a significantly lower frequency of histological abnormalities compared to early-onset disease and absence of a distinctive biochemical profile. The histological placental findings in FGR are therefore varied, from morphologically unremarkable through to severe uteroplacental vasculopathy, with no single pathological feature associated with high sensitivity or specificity. Severe early-onset FGR, overlapping with severe early-onset PET, is mainly associated with features of impaired maternal uteroplacental perfusion secondary to defective extravillous trophoblast invasion, and its consequences. Late-onset FGR probably represents a more heterogeneous group with less characteristic histological changes. Future research using histopathological assessment of aggregated data from multiple studies into larger datasets with centralised pathology review will allow delineation of distinctive clinicopathological associations and further understanding of pathophysiology.