Formation of the placenta and full functioning of the placenta develops at?

PGIMER NO - 2020

Obstetrics & Gynaecology

Easy

Appeared in: PGIMER NO - 2020

Explanation

The formation of the discrete placenta, which involves the differentiation of the chorion frondosum and decidua basalis, begins at approximately the 6th week of gestation.
The placenta is considered structurally complete and fully functional by the 12th week of gestation.
This is when the 'luteal-placental shift' occurs, meaning the placenta takes over the primary role of producing hormones like progesterone from the corpus luteum to maintain the pregnancy.

Option B: While a primitive uteroplacental circulation is established around 3 weeks, this is not the start of the formation of the discrete placenta. At 10 weeks, the placenta is nearing full function but is not yet considered complete.
Option C: At 4 weeks, the cardiovascular system of the embryo is forming, but the discrete placenta has not yet begun to develop. At 8 weeks, the placenta is still developing and has not taken over full endocrine function from the corpus luteum.
Option D: This option is incorrect because a correct timeline is provided in Option A.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The question tests the knowledge of the specific timeline for the formation and functional maturation of the human placenta during pregnancy as background academic context rather than a clinical decision trigger.
Understanding the timeline of placental development is crucial for nurses in antenatal care to interpret early pregnancy ultrasound findings and understand the basis of early pregnancy complications.
Knowledge of the luteal-placental shift around 10-12 weeks helps explain why some early pregnancy symptoms might change and why this period is a critical transition for pregnancy maintenance.
What if? If a patient with a history of recurrent early miscarriages is found to have low progesterone levels at 9 weeks, the nurse would understand this could be related to a failing corpus luteum before the placenta has fully taken over, necessitating potential progesterone supplementation to support the pregnancy until the luteal-placental shift is complete.

How to Approach the Question

First, identify the two key concepts in the question: 'formation of the placenta' and 'full functioning of the placenta'.
Recognize that these are two distinct points in time. 'Formation' refers to the beginning of the development of the discrete organ, while 'full functioning' refers to when it is structurally complete and has taken over its major roles.
Recall the major milestones of early pregnancy. Early circulation starts around 3 weeks. The distinct placenta begins to form around 6 weeks.
Remember the 'luteal-placental shift,' where the placenta takes over hormone production. This critical event is completed by the end of the first trimester, around 12 weeks.
Evaluate the options based on these two time points: formation beginning at ~6 weeks and full function achieved by ~12 weeks. Option A aligns perfectly with this timeline.

Concept Tested & Keywords

Concept Tested: The question tests the knowledge of the specific timeline for the formation and functional maturation of the human placenta during pregnancy.
Stem keywords: Formation of placenta, full functioning of placenta, develops at
Lead-in keywords: BEST, MOST RELEVANT CLUE

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E6 Midwifery Obstetrics and Gynecology Nursing Sandeep Kaur pp. 50-61, 51-62