Placental pathology and clinical trials: Histopathology data from prior and study pregnancies may improve analysis

Placental pathology may explain adverse outcomes and reveal likely recurrent lesions. Stratifying women into intervention arms of a perinatal trial on the basis of the placental histopathological findings of the index pregnancy and evaluating the effect of the interventions against the placental findings at conclusion of a trial may enhance the trial. The Cochrane Central Register of Controlled Trials with "obstetrics" or "perinatal" in the Title, Abstract, or Keywords published in 2015 were classified as to whether placental pathological findings from a previous pregnancy could have been used to stratify the women into the trial and placental pathology (findings) at the end of the study trial could have explained differences in the trial results, and whether these were performed. Two hundred and twenty three of the 275 studies were not relevant. Placental pathology was an outcome measure in 2 of the remaining 52 studies. Seven trials could have benefitted by stratifying women based on previous placental pathology findings, and placental pathology findings at the end of the trial could have explained the trial results but in none of them were these performed. There were 30 trials where placental pathology could have provided an explanation for the result but review of the pathology was not undertaken in any. In the remaining 13 trials, placental pathology was unlikely to be an influence before or after the trial; however, placental pathology would have been of interest or be indicated in most of them. Placental pathology appears to be omitted from perinatal clinical trials. Seventy-four percent (37 of 50) could have benefitted by using placental pathology results of a prior pregnancy to stratify women into intervention arms or incorporating placental pathology results in the evaluation of the interventions.