H2AC21 and fetal growth restriction: Based on these differentially expressed ubiquitinated peptides, three increased and four decreased probable ubiquitinated proteins in IUGR d1 group were identified compared with control d1 group, including DNA damage-inducible 1 homolog 2 (DDI2), 14-3-3 protein gamma, histone H3, histone H2A (Hist2h2ab), histone H2A (H2afx), moesin, and lysozyme, respectively.