● preembryonic period(胚前期): before2weks IL embryonic period(胚期):38 weeks 周 4周 周 8周 ● fetal period(胎儿期): after9 Weeks 9周16周 20-3638周embryonic period（胚期）: 3-8 weeks fetal period（胎儿期）: after 9 weeks preembryonic period（胚前期）: before 2 weeks