Most vulnerable period for teratogenicity during fetal development is
The preimplantation period is the 2 weeks from feilisation to implantation and is known as the "all or none" period. As the zygote undergoes cleavage, an insult damaging a large number of cells typically causes embryonic death.However if few cells are injured compensation may be possible, with normal development. The embryonic period is from the 2nd -8th week post feilisation, encompasses organogenesis and is thus the most critical period with regard to structural malformations. The fetal period, which is beyound 8 weeks, is characterised by continued maturition and functional development and during this time, ceain organs remain vulnerable. Reference: William's Textbook of Gynaecology 4th edition page 242
1st and 2nd week post feilization
3rd to 8th week post feilization
10th to 12th week post feilization
18th to 20th week post feilization
General obstetrics