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Genetics and Fetal Development

Genetic Basis of Pregnancy

Chromosome abnormalities during pregnancy

Origin: gametogenesis, fertilization, post-zygotic cleavage

Consequences: preimplantation death, implantation failure, SAB

Classes of chromosome aberrations (CA)



Structural rearrangements

Aneuploidy during pregnancy Aneuploid oocytes: 15-30% 2. Aneuploid spermatozoa: 3%

Fertilization-related CAs: 8%

Aneuploid preimplantation embryos: 24%

Aneuploid first trimester embryos: 15-25% 6. Aneuploid 2nd and 3rd trimester fetuses: 7% 7. Aneuploid newborns: 0.3-0.5%

Structural congenital malformations: 4%

Mental retardation: 12%

Congenital heart defects: 13%

Types of CAs during pregnancy


45, X: 28%

Trisomy 16: 31%

Trisomy 18: 5%

Trisomy 21: 8%

Trisomy 22: 10%

down syndrome, downs

Structural rearrangements: 5.1%

Risk of trisomy conception following abortion of unknown karyotype

Risk of subsequent trisomy abortion: 4.5%

Risk of subsequent trisomic liveborn: 0.45%

Risk of trisomic offspring subsequent to trisomic abortion: 0.5%

II. Chromosome Aberrations as a Cause of Congenital Malformations

Gene Mutations as a Cause of Congenital Malformations