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 the Broad Institute (Cambridge, Massachusetts, USA) for sequencing. Samples were rechecked for quality at the Broad Institute using the Caliper Life Sciences LabChip GX system to determine an RNA Quality Score (RQS) for each sample, which ranged from 3.3 to 7.8 across all samples (average RQS 5.9). All samples with an RQS value of 4 or higher were submitted for RNA sequencing, and 250ng of each sample underwent library preparation, using an automated variant of the Illumina TruSeq Stranded mRNA Sample Preparation Kit (Illumina, cat RS-122-2103). Flowcell cluster amplification and sequencing were performed according to the manufacturer's protocols using the Illumina HiSeq 4000, to generate 101-bp paired end reads, average of 113M total reads (range 33M to 378M) per sample.