OBSERVER RELIABILITY IN ASSESSING PLACENTAL MATURITY BY HISTOLOGY

Aims-To evaluate the ability of five experienced perinatal pathologist s to assess placental maturity reliably by histology. Methods-Twenty f our haematoxylin and eosin slides, six each from placentas of 27, 31, 35, and 39 weeks' gestation, were circulated to five pathologists on t hree separate occasions. The slides were labelled with the correct or incorrect gestational ages. Results-The mean absolute error over all 3 60 readings was 2.72 weeks. Only 54% of the slides were assessed withi n two weeks of the correct gestation. Pathologists tended to overestim ate younger gestations and underestimate older gestations. Two, and po ssibly three, pathologists were influenced by the gestational age stat ed on the label. One pathologist, who did not appear to be influenced by the label, was more accurate in diagnosing gestation of the placent as than other colleagues. Conclusions-Experienced pathologists can hav e difficulty in assessing the villous maturity of placentas by histolo gy. They can also be influenced by clinical information provided, such as gestational age. Other observer reliability studies must address t he issue of the influence of labelled information on observer variatio n. A difference in maturation would have to be of a six week magnitude to have a chance of being detected by current methods. This may limit the value of the histological diagnosis of placental dysmaturity as a surrogate marker for uteroplacental ischaemia.