Decidual spiral artery remodelling begins before cellular interaction with cytotrophoblasts.

Endometrial arteries undergo structural alterations during pregnancy to increase blood flow to the intervillous space. It is hypothesized that physiologic change in decidual arteries is similar to vascular remodelling seen in other organs. Histologic features of spiral arteries in secretory endometrial biopsies were compared blindly to decidual arteries from elective abortions. Similar sections were stained for trophoblastic and vascular antigens. Spiral arteries in endometrium from ectopic (tubal) and intrauterine pregnancies were compared also. Evidence of decidual endothelial activation was sought using antibodies to vascular cell adhesion molecule (VCAM-1). As expected, decidual arteries were significantly different than arteries in secretory endometrium: there was more endothelial basophilia, vacuolation, and arterial dilation in early pregnancy. Some vessels had disorganized or hypertrophied smooth muscle layers. Similar structural alterations were seen in endometrium of ectopic pregnancies, and in the decidua parietalis of intrauterine pregnancies. Immunohistochemical studies confirmed that these alterations occurred in the absence of cellular interaction with extravillous cytotrophoblasts. Independently of trophoblasts, decidual endothelial cells expressed VCAM-1. It is concluded that the initial stages of physiologic change are characterized by vascular remodelling, which occur in the absence of trophoblast invasion of the spiral arteries. Arterial modifications in decidua begin as a maternal response to pregnancy.