Obstetrics and Gynecology - A.M. Hromova 2000

Fertilization and Fetal Development
Development of the Zygote
Critical Periods of Fetal Development

During intrauterine fetal development, A number of critical periods are distinguished. The first critical period of development is considered to be the time preceding and coinciding with implantation. The second is the period of formation of organ and system rudiments in the embryo (3–7 weeks of development) and The process of Placenta formation (9–12 weeks of Pregnancy). The impact of damaging factors During the first critical period leads to the death of the embryo (embryotoxic effect). Damage to the embryo during Organogenesis contributes to The Development of fetal malformations (teratogenic effect), while an embryotoxic effect occurs less frequently. Susceptibility to Congenital Malformations varies depending on the pregnant woman's genotype through which she interacts with the environment, as well as the concentration of the teratogen and the route of its penetration into the fetus. In addition to embryotoxic and teratogenic effects, damaging factors can cause disorders in the fetoplacental complex, leading to prenatal dystrophy of the intrauterine fetus (see Chapter 36).