The most common cause of non-engagement at term in primigravida is?

AIIMS Patna NO - 2020

Obstetrics & Gynaecology

Easy

Appeared in: AIIMS Patna NO - 2020

Explanation

Cephalopelvic disproportion (CPD) is the most frequent reason for a non-engaged fetal head in a first-time mother at term.
CPD signifies a size mismatch between the fetal head and the maternal pelvis, creating a mechanical barrier to descent.
In a primigravida, the fetal head is normally expected to engage in the pelvis by 36-38 weeks; its failure to do so is a classic indicator of potential CPD.
While other factors can cause non-engagement, CPD is the primary and most common underlying cause that must be ruled out.

Option B: In a breech presentation, the fetal buttocks or feet present first, not the head. Therefore, this isn't a failure of a vertex (head-first) presentation to engage, but rather a different presentation altogether.
Option C: Hydramnios (or polyhydramnios) involves an excessive amount of amniotic fluid, which can cause the fetus to float high above the pelvic inlet. While it is a cause of non-engagement, it is not considered the most common primary reason compared to the mechanical obstruction of CPD.
Option D: A brow presentation is a rare form of malpresentation where the fetal head is partially extended. The presenting diameter is the largest possible, which prevents engagement. However, because it is an uncommon event (occurring in about 1 in 500 to 1 in 1000 births), it is not the 'most common' cause.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Causes of fetal non-engagement in primigravida at term as background academic context rather than a clinical decision trigger.
A nurse's abdominal palpation (Leopold's maneuvers) and assessment of fetal station are critical skills. Identifying a non-engaged head in a primigravida at term is a key finding that must be communicated to the provider for further evaluation.
Suspected CPD often leads to further diagnostic imaging like pelvimetry or careful assessment during a 'trial of labor' to determine if a vaginal birth is possible.
A confirmed diagnosis of CPD is a major indication for a Cesarean section to prevent complications of obstructed labor, such as uterine rupture, fetal distress, and maternal exhaustion.

How to Approach the Question

First, identify the key elements of the question: 'most common cause,' 'non-engagement,' 'at term,' and 'primigravida.'
Recall the normal physiology of labor for a primigravida: the fetal head is expected to descend and engage in the pelvis before labor begins, typically by 36-38 weeks.
Understand that 'non-engagement' at term in this context implies a problem preventing this expected descent.
Evaluate each option based on its prevalence and mechanism:
Cephalopelvic disproportion (CPD) is a direct mechanical block due to a size mismatch. This is a primary and logical reason for failure to engage.
Breech presentation is a different fetal lie, not a failure of a head-first presentation to engage.

Concept Tested & Keywords

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E6 Midwifery Obstetrics and Gynecology Nursing Sandeep Kaur p. 51-62

E6 Obstetrics Williams p. 37-56