library_construction_protocol: Placental tissues were collected immediately after abortion, stored in RNAlater solution at 4 °C for 12–16 h and then stored at -80 °C. RNA was harvested using Trizol reagent. KAPA Stranded RNA-Seq Library Prep Kit (Illumina) was used with 1 ug of total RNA for the construction of sequencing libraries. Libraries were prepared by using KAPA Stranded RNA-Seq Library Prep Kit(Illumina). Briefly,Total RNA of each sample was used to prepare the RNA sequencing library 1)RNA fragment；2)Random primed first strand cDNA synthesis；3)dUTP based second strand cDNA synthesis;4)Adaptor ligation and PCR amplification.