Figure 2 The relationship between level of maternal preoperative hemoglobin and risk of massive intraoperative hemorrhage. (The statistical software package R [http://www.R-project.org, The R Foundation] and Empower Stats [http://www.empowerstats.com, X&Y Solutions, Inc., Boston, MA]). The horizontal coordinate presents the level of maternal preoperative hemoglobin, and the ordinate presents the risk of massive intraoperative hemorrhage (0, referred to non-massive intraoperative hemorrhage; 1, referred to massive intraoperative hemorrhage). A non-linear relationship between the level of maternal preoperative hemoglobin and risk of massive intraoperative hemorrhage was detected after adjusting confounders.