Teratogens produce all or none effect till which day of gestation?

Ans. is 'b' i.e., 31 Timing of Teratogen exposure and The hazardsBefore D 31: Teratogen produces an all or none effect. The conceptus either does not survive or survives without anomalies. In early conception only few cells are there. So any damage at that phase is irreparable and is lethal.D 31-D 71 is the critical period for organ formation. Effects of teratogen depend on the following factors: (i) Amount of the drug reaching the fetus, (ii) Gestational age at the time of exposure, (iii) Duration of exposure.After D 71 development of other organs continues. Diethylstilbestrol (DES) related uterine anomalies occur with exposure around 20 weeks.Brain continues to develop throughout pregnancy and neonatal period. Fetal alcohol syndrome occurs in late pregnancy.