design: Placenta biopsies were collected at delivery from participants in the Gen3G cohort. One cm3 placental tissue sample was collected from the maternal and fetal facing side (within 5 cm radius of corresponding location of cord insertion). Each collected sample was immediately put in RNA Later for at least 24 hours before storage at -80C until RNA extraction. Laboratory personnel extracted total RNA (Average 19.7 s.d. 7.1 ug) and checked the quality of each sample using an Aligent Bioanalyzer to determine the RNA Integrity Number (RIN; average RIN 6.7 s.d. 0.8). For samples with a RIN value of 5 or higher, 3ug of each sample was shipped to Novogene (Wayne, New Jersey, USA). Samples have been rechecked for quality at Novogene (average RIN 5.7 s.d. 1.1). Unique Molecular Index (UMI) were assigned during library preparation by Novogene using Qiagen Small RNA Kit. Small RNA sequencing was performed using the Illumina NovaSeq 6000, to generate 75-bp single-end reads.