This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Tests of Ovulation, Subject name: Gynaecology & Obstetrics
[{'content': 'Which of these is an easy and yet a reliable test of ovulation ? \nSelect and explain. \nA. Basal body temperature, B. Vaginal cytology, C. Serum Progesterone level, D. Endometrial biopsy', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Easy and reliable method : Serum progesterone levels Serum progesterone level: a simple blood test done at D21 or 7 days before expected menses. A value of >= 3 ng suggests ovulatory cycle Basal Body temperature: easy but not very reliable, as body temperature may vary for various reasons Vaginal cytology: involves taking a vaginal smear and its microscopy for calculating ratio of parabasal, intermediate and superficial cells, therefore not a very easy test to perform, although it is reliable Endometrial biopsy: most reliable test, tells about secretory changes in endometrium, but not the easiest test', 'role': 'assistant'}]