The United States is one of the pioneers in the world to introduce a heath strategy, making its practice highly significant for other countries. The paper described the four health strategies developed by the US government in succession, including the goals, focused areas and key health indicators of the strategies in different stages. In addition, it analyzed the patterns of evolution and key features of the strategy, offering references for the development and implementation of the "Health China by the Year 2020".

8 oocytes) according to the number of oocytes collected in one ovary. On day of human chorionic gonadotrophin injection, PSV, EDV, PI, RI, S/D of ovarian stromal artery in the ovarian were detected and perifollicular vascularity were graded with color Doppler ultrasonography. Results Not only PSV and EDV of stromal artery but also perifollicular vascularity in low-response group was significantly lower than that of normal-response and high-response groups. PSV and EDV of ovarian stromal artery and perifollicular vascularity were highly interrelated with ovarian response. Conclusions The increase of PSV and EDV of ovarian stromal artery and perifollicular vascilarity indicate the improvement of perfusion in ovary and ovarian response.