<prompt> Chorionic villus biopsy is done in all of the following EXCEPT:Neural tube defectsSickle cell diseaseMyotonic dystrophyDown syndrome  <response>: Ans. A. Neural tube defectsa. Indications of Chorionic villus biopsy:i. Karyotyping is the most common indication--Down syndromeii. Hemoglobinopathies --Sickle cell disease, Thalassemia, etc.iii. Biochemical studies--Gauchers disease, Niemann-Pick disease, Tay-Sachs disease, etc.iv. Single gene defects--Myotonic dystrophy, Cystic fibrosis, Huntingtons disease, Phenylketonuria, etc.b. Neural tube defects are diagnosed by ultrasound and estimation of alpha-fetoprotein in maternal serumamniotic fluid.c. Chorionic villous biopsy can be done after 10th week earlier than amniocentesis i. Earlier results reduce maternal stress by going for a possible therapeutic abortion if indicated at an early stage.d. Initially a trans-cervical route is acceptable to take the sample.i. A trans-abdominal route is taken if the pregnancy exceeds 12th week. 