Alternative polyadenylation (APA) affects the length of the 3' untranslated region (3'-UTR) and the regulation of microRNAs. Previous studies have shown that cancer cells tend to have shorter 3'-UTRs than normal cells. A plausible explanation for this is that it enables cancer cells to escape the regulation of microRNAs. Here, we extend this concept to an opposing context: changes in 3'-UTR length in the development of the human preimplantation embryo. Unlike cancer cells, during early development 3'-UTRs tended to become longer, and gene expression was negatively correlated with 3'-UTR length. Moreover, our functional enrichment results showed that length changes are part of the development mechanism. We also investigated the analogy of 3'-UTR length variation with respect to lncRNAs and found that, similarly, lncRNA length tended to increase during embryo development. (C) 2018 Elsevier Inc. All rights reserved.