Fig. 1

This is the flow chart of this study. Steps with superscript (labeled as a, b, c, d) were explained as following. a Only the first cycle of couples with more than one stimulation cycles was included in the final analysis. b The reason of induced abortion was fetal abnormality diagnosed by amniocentesis (8 cases) and unknown (3 cases). c One woman had twin pregnancy, but one of the fetus was missed before 12 gestational weeks. d Two women had twin pregnancy and both had elective embryo reduction in the first term of pregnancy