This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
At what period, Frequency is present in pregnancy: 
Select and explain. 
A. Before 16 weeks, B. After 18 weeks, C. After 20 weeks, D. After 24 weeks
A: Before 16 weeks
Answer: A: Before 16 weeks 
Explanation: Before 16 weeks