Ans. is b, i.e. Mortality rate of 20% with undiagnosed caseRef Williams Obs 23/e, p 583-584, High risk pregnancy" Fernando Anas 3/e p 348, progress in Obs. and Gynae- John Studd vol. 17/e p 209Vasa previa: It is a condition in which the fetal blood vessels unsupported by either umbical cord or placental tissue, overlies the internal os and is vulnerable to rupture when supporting membrane rupture.Thus bleeding in case of vasa previa is of fetal origin and not maternal origin (unlike placenta previa and abruptio)It is rare condition and occurs in 1 in 2000 - 3000 deliveries (i.e. option ais correct).Vasa previa should be suspected if any of the following condition exists-Velamentous cord insertion-Bilobed placenta-Succenturiate lobed placenta-Placenta previa/low lying placenta in second trimester (option 'c' is correct)-Pregnancy resulting from IVF-Multiple pregnanciesVasa previa is associated with high fetal mortality - (75-100%) because---Wharton's jelly is absent around the fetal vessels, hence they can be easily lacerated at the time of rupture of membranes leading to severe fetal bleeding.-Vessels can be easily compressed by the fetal presenting part during uterine contractions leading to fetal exsanguination.This explains that option b i.e. mortality rate is 20% in undiagnosed case is incorrect (mortality is 75-100%)Maternal mortality is not increasedDiagnosis of vasa previa - In all cases of antepartum and intrapartum hemorrhage, the possibility of vasa previa should be kept in mind and blood should be tested for fetal hemoglobin characterized by resistance to denaturation by alkaline reagent (Singer alkali denaturation test/Apt test)Doppler examination can also reveal fetal blood vessels traversing below the presenting partManagement: In a diagnosed case of vasa previa elective cesarean section should be done or emergency LSCS should be done if it is diagnosed intrapartum.