This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Physiology & Histology, Subject name: Gynaecology & Obstetrics
In 40 days of menstrual cycle the ovulation occurs at: 
Select and explain. 
A. 14th day, B. 20th day, C. 26th day, D. 30th day
C: 26th day
Answer: C: 26th day 
Explanation: Ans. is c, i.e. 26th dayRef Shaw 15th/ed, p30* Ovulation is estimated to occur 14 days before the first day of succeeding cycle and this interval is fixed.* In case of irregular cycles, it is the follicular phase which varies, but the luteal phase remains more or less constant at 14 days, therefore day of ovulation can be estimated by counting 14 days backward.* As in the question the cycle is of 40 days, ovulation will occur 14 days prior to next menstruation i.e. (40-14)=26 dayRemember = Day of ovulation = Length of Menstrual cycle - 14