Question

Implantation occurs on which menstrual cycle day?

• A. 5-7 days
• B. 20-22 days
• C. 14-18 days
• D. 26-28 days

Hint:

Ovulation is day 14; add 6-7 days of pre-implantation development.

Answer 1

The Correct Option is B

Step 1: The question gives the day of the menstrual cycle, not the day after fertilization. To answer it you must add the events of the cycle together.

Step 2: In a standard 28 day cycle, ovulation occurs on day 14, and fertilization takes place within about 24 hours of ovulation, so around day 15.

Step 3: Implantation of the blastocyst happens about 6 to 7 days after fertilization. Adding 6 to 7 days to day 14-15 brings you to roughly day 20 to 22 of the menstrual cycle.

Step 4: Therefore implantation corresponds to menstrual cycle days 20-22, option b. Option a (5-7 days) is the post-fertilization interval, not the cycle day, and the other options do not match the timing.