Ans. is 'a' i.e., 6-12 weeks of pregnancy Congenital rubella syndrome (CRS) refers to infants bom with defects secondary to intra uterine infection or who manifest symptoms or signs of intrauterine infection sometimes after birth.Rubella infection inhibits cell division and this is probably the reason for congenital malformations and low birth weight.Always remember these important points about congenital rubella infection.The fetus can be infected as well as affected in all stages of the pregnancy.The rate of infection as well as damage to the fetus is highest during first trimester.* Both the risk of infection as well as risk of damage to the fetus goes on decreasing as the pregnancy progresses, so the rate of infection and the risk of damage to the fetus is lowest in 3rd trimester.Stage of gestation (weeks) when mother gets infectedPercentage of fetuses infectedPercentage of infected fetuses damagedOverall risk of damage to fetus (percent)< 11901009011-2655372017-26330027-365300