This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intra Uterine Growth Restriction, Intrapaum and Antepaum Fetal Surviellance, Subject name: Gynaecology & Obstetrics
[{'content': 'Cordocentesis is done in which period of pregnancy? \nSelect and explain. \nA. 11-14 weeks, B. 18-20 weeks, C. 26-28 weeks, D. 28-32 weeks', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Cordocentesis or percutaneous umbilical blood sampling (PUBS)- Done after 18 weeks Invasive procedure Gives results in 24-48 hrs punctured near the inseion at the placental end Uses - Fetal anemia assessment remains the most common indication. Assessment and treatment of platelet allo-immunization and for fetal karyotype determination', 'role': 'assistant'}]