Methods to improve the reliability of histopathological diagnoses in the placenta

The interobserver reliability of histopathological features in the placenta was examined. Two pathologists independently reviewed slides from 250 plac entas. The pathologists were given a morphological description of the place nta, but were blinded to clinical status, gestational age and original diag noses. A protocol for diagnosis and grading of features was first developed and pilot-tested. Definitions and criteria were refined and elaborated. A range of features was examined including inflammatory lesions, features ind icative of reduced uterine blood flow and other miscellaneous histopatholog ical changes. Weighted kappa coefficients were calculated. The effect of mu ltiple features on reliability was examined by stratifying on the presence of a second feature and calculating stratum-specific kappa coefficients. Re sults indicated good to excellent agreement for diagnoses of chorioamnionit is, cord vasculitis, funisitis and villitis (kappa(w) range 0.70-0.83). Agr eement between observers was more variable for the diagnosis of reduced ute rine blood flow states. Excellent agreement was observed for the diagnosis of meconium staining of the placenta (kappa(w) = 0.79). In general, lower l evels of agreement were observed for features in the presence of a second f eature. Reproducible measures are a prerequisite to using placental histopa thology for diagnostic and prognostic information. This study demonstrated reliable placental diagnoses can be achieved through a standardised protoco l.