Intervillous connections in the mature human placenta: instances of syncytial fusion or section artifacts?

In order to investigate the nature of apparent intervillous syncytial connections in the normal mature human placenta, 250 examples were followed through plastic serial sections at 2 micron intervals. It was possible to classify them into four types according to their origin. Type 1 (20%): section through an area of syncytial fusion or genuine bridge; Type 2 (53%): tangential section through the syncytium filling the crotch of a villus branching point; Type 3 (4%): tangential section through the syncytium lining the internal angle of a tight 'U' bend of a villus; Type 4 (23%): tangential section through the syncytium of a sinuous villus. It is clear, therefore, that whilst areas of syncytial fusion do occur between adjacent villi, the majority of supposed intervillous connections seen in sections are artifacts.