Question:hard
Establishment of the fetoplacental circulation is seen at which day after fertilization?
Establishment of the fetoplacental circulation is seen at which day after fertilization?
Show Hint
Tertiary villi and the first fetal heartbeat appear around day 21 - that starts the fetoplacental circulation.
Updated On: Jun 23, 2026
- 11 to 13 days
- 20 to 22 days
- 7 days
- 25 to 26 days
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: Distinguish two circulations: the uteroplacental (maternal) circulation forms early when trophoblasts erode endometrial vessels, while the fetoplacental circulation needs a beating fetal heart plus vascularised villi. Step 2: Track villus maturation - primary villi at about day 13, secondary at about day 16, and tertiary villi (containing fetal capillaries) at about day 21. Only tertiary villi can carry the fetal circulation. Step 3: The fetal heart first contracts and the fetoplacental loop is completed around the 21st to 22nd day, placing the answer in the 20 to 22 day band. Step 4: Day 7 is just blastocyst attachment, days 11 to 13 cover early uteroplacental circulation and primary villi, and day 25 to 26 is past the standard milestone, so option b is correct. \[\boxed{\text{20 to 22 days}}\]
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