This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contraception, Subject name: Gynaecology & Obstetrics
What is the minimum dose of ethinyl estradiol in OC pills for contraceptive effect? 
Select and explain. 
A. 15mcg, B. 20mcg, C. 30mcg, D. 35mcg
B: 20mcg
Answer: B: 20mcg 
Explanation: For the average patient, the first choice of preparation for contraceptive purposes is a very low estrogen OC (20 mg EE) unless there are other considerations, for example, previous pregnancy while taking the pill.Patients with persistent break-through spotting or bleeding could be offered a pill with the same low estrogen dose, but a more potent progestin, for example, levonorgestrel.Ref: Reference: Novak's gynaecology; 14th edition; Chapter 10; Family planning