Ans. is 'a' i.e., First trimester of pregnancy In general, the earlier in pregnancy infection occurs, the greater the damage to the fetus. Maximum damage to the fetus occurs when infection is acquired in the first trimester of pregnancy.Rubellao Rubella virus belongs to togavirus family - enveloped RNA virus .o Only one antigenic type of virus exists,o Source of infection - clinical or sub-clinical case.o A large number of rubella infections are sub-clinical, this represents one of the major differences between measles and rubella.o There is no known carrier state in postnatally acquired rubella, but infants bom with congenital rubella may shed virus for many months.o Infective period - A week before the onset of symptoms to about a week after rash appears,o Rubella is much less communicable than measles because of absence of coughing in rubella,o Age group -3-10 vears.o Transmission -Droplet infection by respiratory route.Vertical transmission from mother to fetus.o Incubation period - 2-3 weeks.o Clinical manifestationsProdromalLow grade fever, sore throat, coryza.LymphadenopathyPosterior auricular, cervical and sub-occipital.RashBegins on the face and spreads down the body.A petechial exanthem on the soft palate - Forschheimer spots.Complicationso Arthralgiao Encephalitiso Thrombocytopenic purpuraCongenital rubella syndromeo Maternal viremia associated with rubella infection during pregnancy may result in infection of the placenta and fetus.o The most important factor in the pathogenicity of rubella virus for the fetus is gestational age at the time of infection. The earlier in pregnancy infection occurs, the greater the damage to the fetus.Risk of damage to foetus by maternal rubella during pregnancyStage of gestation (weeks) when mother infected (symptomatic plus asymptomatic)Percentage of fetuses infectedPercentage of infected fetuses damagedOverall risk of damages of foetus (per cent)< 1111-1617-2627-36905533531003700902000o Fetus infected in the twentieth week may have isolated deafness,o Clinical manifestationsThe classical triad of congenital rubella consists of cataract, deafness and congenital heart diseases,o Laboratory diagnosisIsolation of virus in cell cultures of throat samples, urine or other secretions.Normally, maternal rubella antibodies in the form of IgG is transferred to infants and is gradually last over a period of 6 months. Persistent beyond 1 year in an unvaccinated child suggests the diagnosis of congenital rubella.Presence of ig M antibodies is diagnostic.PCR for rubella RNA.