At the end of which week after fertilization the embryo is considered a foetus? Choose the closest option.

MP NHM CHO-2024 (Shift-1)

Obstetrics & Gynecology

Easy

Appeared in: MP NHM CHO-2024 (Shift-1)

Explanation

The transition from the embryonic to the fetal period occurs at the end of the 8th week after fertilization.
The embryonic period, spanning from the 3rd to the 8th week, is the critical time for organogenesis, where all major organ systems are established.
From the beginning of the 9th week until birth, the developing human is referred to as a fetus.
The fetal period is characterized by rapid growth and maturation of the already-formed organ systems.

Option A: The 3rd week marks the beginning of the embryonic period, characterized by gastrulation and the formation of the three primary germ layers. It is not the point of transition to a fetus.
Option C: By the 15th week, the developing human is already well into the fetal period. Organogenesis is complete, and the focus is on growth and maturation.
Option D: The 36th week is very late in pregnancy, considered early term. The fetus is almost fully developed and ready for birth.

Visual 1: Infographic - A timeline illustrating the key stages of prenatal development. It should clearly mark the Zygote/Blastocyst (0-2 weeks), Embryonic (3-8 weeks), and Fetal (9 weeks to birth) periods, with a prominent label at the 8-week mark indicating the transition from embryo to fetus.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Stages of prenatal development, specifically the transition from embryo to fetus as background academic context rather than a clinical decision trigger.
The distinction between the embryonic and fetal periods is clinically crucial because the embryo is most susceptible to teratogens (agents causing birth defects) during the 3rd to 8th weeks, as this is when major organs are forming.
This knowledge is vital for nurses when counseling pregnant women on medication safety, avoiding alcohol and certain infections, and understanding the timing of prenatal screening tests.
What if? If a woman is exposed to a known teratogen (like high-dose radiation) at 6 weeks post-fertilization, there is a high risk of major structural anomalies. If the same exposure occurs at 12 weeks, the risk shifts towards functional deficits, growth restriction, or central nervous system issues, as the primary structures are already formed.

How to Approach the Question

This is a factual recall question testing knowledge of embryology.
Identify the key terms in the question: 'embryo', 'foetus', and 'end of which week'.
Recall the specific definitions and timeframes for the major stages of prenatal development.
Remember that the embryonic period is defined by organogenesis (organ formation).
Remember that the fetal period is defined by growth and maturation of these formed organs.
The transition point occurs when organogenesis is largely complete, which is at the end of the 8th week after fertilization.

Concept Tested & Keywords

Concept Tested: Stages of prenatal development, specifically the transition from embryo to fetus.
Stem keywords: fertilization, embryo, foetus, week
Lead-in keywords: end of which week

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