Abstract:

Monozygotic twins originate from the early division of a single fertilized egg, theoretically possessing genetic homogeneity and consistency in the intrauterine environment, resulting in a high degree of phenotypic similarity. However, the observed inconsistencies in monozygotic twins pregnancy in clinical practice, such as one fetus developing normally while the other exhibits developmental abnormalities, suggest potentially complex mechanisms. By reviewing domestic and international literature, this paper summarizes the causes of these differences, including genetic factors such as mosaicism, de novo mutations, and chromosomal copy number variations, epigenetic factors covering differential DNA methylation and skewed X-chromosome inactivation, and intrauterine environmental factors involving gut microbiota and amniotic fluid environment, among others. For different disease phenotypes, clinical interventions such as elective fetal reduction, termination of pregnancy, or expectant management can be adopted. Reviewing the literature has enhanced the understanding of the developmental inconsistencies in monozygotic twins, which provides a scientific basis for the early prevention, diagnosis, and treatment of fetal diseases, and holds clinical guidance significance.

Key words: Diseases in twins, Twins, monozygotic, Fetal development, Phenotype, Genes, Epigenomics, Intrauterine environment, Early medical intervention