deficits. xv P'art I Physio-anatom-ical Parameters 1 Uterine microvasculature and spontaneous abortion M. TAKADA In the implantation and subsequent development of a fertilized ovum, its integrity is most significant. However, with maternal local factors, i.e., unsatisfactory uterine conditions, implantation may not succeed even if the integrity of the fertilized ovum is excellent; if implantation is made, the maturation of the fetoplacental unit following implantation is disturbed, which leads to abnormalities in fetal development or to miscarriage. Thus, the uteroplacental unit, as well as the fetoplacental unit, plays an important role in the establishment and maintenance of pregnancy. Among the mechanisms of the utero placental unit, most significant is the physiological mechanism of the uterine microvasculature and its correspon­ dence to gestation. In particular, homeostasis of simultaneous cooperative development of the uterine wall and the placenta is most important.