PLACENTAL TROPHOBLAST DEVELOPMENT AND VASCULARIZATION During human and nonhuman primate pregnancy, the placenta simultaneously accesses the maternal blood and develops a vascular network for the transport of nutrients to and waste products from the fetus across the syncytiotrophoblast to ensure fetal growth and development. Both processes depend on the ability of the primordial stem-cell cytotrophoblasts to take either the villous pathway where they remain in the fetal compartment and differentiate morphologically into the syncytiotrophoblast or the extravillous pathway where they proliferate, aggregate into cell columns of the anchoring villi, and invade the endometrial stroma (Fig. 6). 105 The syncytiotrophoblast covers the floating chorionic villi that become highly vascularized, whereas the extravillous cytotrophoblasts infiltrate the walls of the spiral arterioles to facilitate the process of placentation.
The adverse effects of corticosteroids in pediatric patients are similar to those in adults (see ADVERSE REACTIONS ). Like adults, pediatric patients should be carefully observed with frequent measurements of blood pressure, weight, height, intraocular pressure, and clinical evaluation for the presence of infection, psychosocial disturbances, thromboembolism, peptic ulcers, cataracts, and osteoporosis. Pediatric patients who are treated with corticosteroids by any route, including systemically administered corticosteroids, may experience a decrease in their growth velocity. This negative impact of corticosteroids on growth has been observed at low systemic doses and in the absence of laboratory evidence of HPA axis suppression (., cosyntropen stimulation and basal cortisol plasma levels). Growth velocity may therefore be a more sensitive indicator of systemic corticosteroid exposure in pediatric patients treated with corticosteroids should be monitored, and the potential growth effects of prolonged treatment should be weighed against clinical benefits obtained and the availability of treatment alternatives. In order to minimize the potential growth effects of corticosteroids, pediatric patients should be titrated to the lowest effective dose.