Disparity in relation between the fetal head and maternal pelvis is called?

NVS Staff Nurse - 2022

Obstetrics & Gynaecology

Easy

Appeared in: NVS Staff Nurse - 2022

Explanation

Cephalopelvic Disproportion (CPD) is the specific term used to describe a mismatch or disparity in the relationship between the fetal head and the maternal pelvis.
This condition occurs when the fetal head is too large to fit through the mother's pelvis, or the pelvis is too small for the fetus, making vaginal delivery difficult or impossible.
CPD is a functional diagnosis, meaning it is often confirmed during labor when there is a lack of fetal descent despite strong uterine contractions.
It is a leading cause of arrested labor and a common indication for Cesarean section.

Option B: Unstable lie refers to the fetus frequently changing its position (lie) within the uterus (e.g., from longitudinal to transverse). It describes the orientation of the fetus, not a size mismatch between the head and pelvis.
Option C: A contracted pelvis is an anatomical condition where the pelvis itself is smaller than normal in one or more of its key diameters. While it is a major cause of CPD, it is not the definition of the disparity itself. CPD can occur even with a normal-sized pelvis if the fetus is very large (macrosomia).
Option D: Malposition refers to an abnormal position of the fetal head in relation to the maternal pelvis, such as an occipito-posterior (OP) position. This can cause a 'functional' CPD by presenting a larger head diameter, but it is a cause of the disparity, not the definition of the disparity itself.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Cephalopelvic Disproportion (CPD) and related obstetric terminology as background academic context rather than a clinical decision trigger.
Recognizing the potential for CPD is crucial in labor management. Nurses monitor the progress of labor using a partograph, paying close attention to the rate of cervical dilation and fetal descent. Failure to progress is a key sign of potential CPD.
CPD is a primary indication for performing a Cesarean section to ensure the safety of both the mother and the baby, preventing complications like uterine rupture, birth trauma, and fetal distress.
What if? - If a woman has a normal-sized (gynecoid) pelvis and a fetus of average weight, but labor arrests, the cause could be a malposition (like occipito-posterior). This creates a 'relative' CPD. Management might involve allowing more time for the head to rotate, maternal position changes, or proceeding to an operative vaginal delivery or C-section if rotation does not occur.

How to Approach the Question

First, identify the key terms in the question: 'disparity,' 'fetal head,' and 'maternal pelvis.' This points directly to a problem of mismatch or disproportion.
Analyze the term 'Cephalopelvic Disproportion' (CPD). Break it down: 'Cephalo-' refers to the head, 'pelvic' refers to the pelvis, and 'disproportion' means a mismatch in size or relationship. The term itself is a literal definition of the condition described.
Evaluate the other options. 'Contracted pelvis' describes a small pelvis, which is a cause of CPD. 'Malposition' describes an incorrect fetal head position, which is also a cause of CPD. 'Unstable lie' describes the overall orientation of the fetus in the uterus.
Differentiate between the condition itself (the disparity) and its potential causes. The question asks for the name of the disparity, not its cause.
Conclude that CPD is the most accurate and direct term for the mismatch between the fetal head and maternal pelvis.

Concept Tested & Keywords

Concept Tested: Cephalopelvic Disproportion (CPD) and related obstetric terminology.
Stem keywords: disparity, fetal head, maternal pelvis
Lead-in keywords: is called
Negative lead-in flag: false

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E6 Midwifery Obstetrics and Gynecology Nursing Sandeep Kaur pp. 51-62, 50-60

E6 Obstetrics Williams p. 33-54