Fetal lung samples at 12–20 post conception week (pcw) from the HDBR, up to 0.5cm3 in size, were embedded in OCT and flash-frozen in dry-ice cooled isopentane. Twelve-micron cryosections were cut onto Visium slides, haematoxylin and eosin stained and imaged at 20X magnification on a Hamamatsu Nanozoomer 2.0 HT Brightfield. These were then further processed according to the 10X Genomics Visium protocol, using a permeabilization time of 18 min for 12–17 pcw samples and 24 min for 19 pcw and older samples. Images were exported as tiled tiffs for analysis. Dual-indexed libraries were prepared as in the 10X Genomics protocol, pooled at 2.25 nM and sequenced in 4 samples per Illumina Novaseq SP flow cell with read lengths of 28 bp for R1, 10 bp for i7 index, 10 bp for i5 index, 90 bp for R2.