A woman has a 35 days period. On what day should her progesterone level be measured to determine ovulation?
a. Day 14th
b. Day 16th
c. Day 21st
d. Day 25th
e. Day 28th
answer: E
Ovulation is always 14 days before the end of the cycle, you can subtract 14 from the cycle length to find the day of ovulation. This represents the beginning of the luteal phase.
Cycle length - 14 = ovulation day
35 day cycle= beginning of luteal phase/ovulation on day 21
However, we use the Mid-luteal progesterone level to assess ovulation:
The blood test is taken seven days before the anticipated period, that is on day 21 of a 28-day cycle. However, this day will need to be adjusted for different lengths of cycle
For a 35 day cycle:
Ovulation on day 21, luteal phase is day 21 to 35, mid luteal = 28th.
or simply 35 - 7 = 28th