Feto-placental circulation begins from?

PGIMER Sangrur NO - 2023

Obstetrics & Gynaecology

Easy

Appeared in: PGIMER Sangrur NO - 2023

Explanation

Feto-placental circulation is established around the 21st day (end of the 3rd week) after fertilization.
This milestone coincides with the formation of tertiary chorionic villi, which are characterized by the presence of fetal capillaries within them (angiogenesis).
The fetal heart also begins to beat around this time, enabling the pumping of blood through these newly formed vessels to the placenta.
This circulation is completed when the blood vessels of the embryo connect with the chorionic vessels, allowing for nutrient and gas exchange.

Option A: Day 7 marks the beginning of blastocyst implantation into the endometrium. At this stage, the complex vascular network required for feto-placental circulation has not yet developed.
Option B: By day 14, primary and secondary chorionic villi have formed, but they are avascular (lack blood vessels). While uteroplacental circulation is beginning, the fetal side is not yet connected.
Option D: By the 28th day (end of the 4th week), the feto-placental circulation is already well-established and functioning. This is too late for the beginning of the circulation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Timeline of Feto-placental Circulation Development as background academic context rather than a clinical decision trigger.
Understanding this timeline is crucial for nurses in obstetrics to appreciate the critical early stages of pregnancy when the fetus is highly vulnerable to teratogens that can disrupt vascular development.
A failure in the proper establishment of feto-placental circulation can lead to serious complications like early pregnancy loss, intrauterine growth restriction (IUGR), or pre-eclampsia.
This knowledge helps in counseling patients about the importance of avoiding harmful substances (like certain drugs, alcohol, and tobacco) during the very early weeks of pregnancy, often before a woman may even be aware she is pregnant.

How to Approach the Question

This is a factual recall question about a specific timeline in embryology.
First, identify the key concept: the beginning of 'feto-placental circulation'.
Recall the major milestones of early embryonic and placental development. The key event for feto-placental circulation is the vascularization of the chorionic villi.
Associate the start of this circulation with the development of tertiary (vascularized) chorionic villi and the first heartbeat.
Evaluate the given options against this timeline: Day 7 is implantation. Day 14 is too early (avascular villi). Day 28 is too late (circulation is already established).
Conclude that Day 21, which marks the end of the third week, is the correct milestone for the establishment of this circulation.

Concept Tested & Keywords

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E6 Obstetrics Williams pp. 65-88, 19-36