Pathophysiology of histological changes in early pregnancy loss

An early pregnancy loss (EPL) or first-trimester miscarriage is the most common complication of human reproduction, with an incidence ranging between 50 and 70% of all conceptions. Two-thirds of EPL cases present with a thinner and fragmented trophoblastic shell, and reduced cytotrophoblast invasion of the tips of the spiral arteries. This leads to incomplete plugging during early pregnancy, and premature onset of the maternal circulation throughout the placenta. The excessive entry of maternal blood into the intervillous space has a direct mechanical effect on the villous tissue, and an indirect oxidative stress effect that contributes to cellular dysfunction and/or damage. Correlation of in vivo and in vitro data suggests that overwhelming oxidative stress of the placental tissues represents a common pathophysiological mechanism for the different etiologies of EPL. Autosomal trisomies are the most frequent karyotypic abnormalities found in EPL, but the comparison of data from different cytogenetic studies is difficult because of the lack of clinical information in many cases on maternal age, gestational age, time of fetal demise and the cytogenetic methodology employed. The majority of authors did find a weak association between villous morphologic features and chromosomal abnormalities, with the exception of partial mole triploidy. The comparison of ultrasound findings and placental histological data indicates that villous changes following fetal demise in utero could explain the overall low predictive value of placental histology alone in identifying an aneuploidy or another non-chromosomal etiology. By contrast, the histological features of complete and partial hydatidiform molar EPL are so distinctive that most cases of molar EPL are correctly diagnosed by histological examination alone. Overall, histopathology when correlated with in vivo ultrasound/Doppler has provided novel clues to the pathophysiology of EPL. Prospective studies are needed to evaluate the impact of these findings on routine histopathologic examination in first-trimester miscarriages.