The placenta dilemma.

Abstract

Despite the critical role the placenta plays in governing the outcome of pregnancy, a great deal remains to be learned about this transient organ. Several factors have contributed to our relative lack of knowledge. For example, most of the placenta's development, which precedes that of the embryo or fetus, occurs during the first half of pregnancy in humans. Thus, it is difficult to obtain the tissue samples that are required to study relevant time points. In addition, placental anatomy is complex; one of the most interesting parts can be obtained only by biopsy of the uterine wall. Recent analyses of these biopsies, combined with information from cell culture models, revealed the unexpected finding that placental cells that invade the uterus phenocopy many endothelial cell characteristics. This finding has several interesting implications for normal pregnancy and for pregnancy complications that could be related, either directly or indirectly, to this phenomenon, such as preeclampsia and cytomegalovirus transmission.