Histological classification of chorionic villous vascularization in early pregnancy

The objective of the study was to assess the reproducibility of a new classification for early pregnancy chorionic villous vascularization (Grade: I, normal; IIA, mild hypoplasia; IIB, severe hypoplasia and III, avascular) for routine microscopic examination in daily clinical practice.

In this observational study, four observers scored first trimester chorionic villous vascularization. Scoring was performed in microscopic slides of chorionic tissue obtained by D&C in 30 patients with early pregnancy loss due to empty sac (n = 10), fetal death (n = 10) and termination of pregnancy (n = 10) using the new classification. Ultrasonographic measurement of trophoblastic thickness (TT) at the implantation site was available in all patients and in a reference group of 100 ongoing singleton pregnancies. The vascularization score could therefore be related to the TT.

The new classification resulted in a good-to-excellent agreement in histological scoring (0.73-0.90) between investigators (kappa 0.64-0.86). TT was not related to either vascularization or pregnancy outcome and only partly to hydropic degeneration.

The vascularization scoring system is a simple, valid and effective method for assessment of chorionic villous vascularization. It is helpful in understanding the underlying cause of pregnancy loss, as the classification can distinguish between normal and abnormal embryonic development. We did not find either a relation between TT and pregnancy outcome or between TT and vascularization.