When does the posterior fontanel close in the baby?

Appeared in: Combined AIIMS - 2020 (Jodhpur, Bhopal, Patna, Raipur)

Explanation

The posterior fontanelle is the smaller, triangular-shaped soft spot located on the back of an infant's skull.
According to normal developmental milestones, this fontanelle undergoes ossification and closes by 6 to 8 weeks of age.
The time frame of 2 to 3 months provided in the option correctly encompasses this period.

Option B: This timeframe is incorrect for the posterior fontanelle.
Option C: This is too early for the complete closure of the posterior fontanelle.
Option D: This is significantly too early. The fontanelles are necessarily open at birth.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Infant developmental milestones: Fontanelle closure as background academic context rather than a clinical decision trigger.
Nurses must assess fontanelles at each well-child visit. A sunken fontanelle can indicate dehydration, while a bulging fontanelle can suggest increased intracranial pressure.
Delayed closure of the posterior fontanelle (beyond 3-4 months) can be an early sign of certain medical conditions, such as congenital hypothyroidism or hydrocephalus, requiring prompt referral.
What if? If a fontanelle closes prematurely (craniosynostosis), it can restrict brain growth and cause an abnormal head shape, which may require surgical intervention. Therefore, both early and late closure are clinically significant findings.

How to Approach the Question

First, identify the specific anatomical part in the question: the 'posterior fontanel'.
Second, recall the two main fontanelles and their distinct closure times. The posterior (back) closes much earlier than the anterior (front).
Third, access your knowledge of normal infant development milestones. The posterior fontanelle closes within the first few months of life.
Fourth, evaluate the options. '2 to 3 years' is for the anterior fontanelle. 'Weeks' and 'days' are too soon. '2 to 3 months' correctly brackets the typical 6-8 week closure time.

Concept Tested & Keywords

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E6 Comprehensive Textbook of Community Health NursingShyamala D part 1 (pp 26-389 of 389) p. 300-302

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