Doppler effect of ultrasound can pick up foetal heart rate by

RRB Staff Nurse Jaipur-6th June 2018

Obstetrics and Midwifery Nursing

Easy

Appeared in: RRB Staff Nurse Jaipur-6th June 2018

Explanation

The fetal heartbeat becomes audible using a handheld Doppler ultrasound around the 10th to 12th week of gestation.
The Doppler device uses the principle of the Doppler effect, where it detects a frequency shift in sound waves that bounce off the moving structures of the fetal heart.
Before 10 weeks, the fetal heart is typically too small and the sounds too faint to be reliably detected through the maternal abdomen with a handheld device.
The 10th week marks the earliest point in the given options when this detection method becomes consistently feasible.

Option A: At 6 weeks, cardiac activity can be visualized as a flicker on a transvaginal ultrasound, but the heartbeat is not audible with a handheld Doppler.
Option B: At 8 weeks, the fetal heart sounds are still generally too weak to be reliably detected by a handheld Doppler through the maternal abdomen.
Option C: While the fetal heart rate is definitely audible with a Doppler at 12 weeks, the question asks for the earliest time it can be picked up. The 10-week mark is the beginning of this window.

Visual 1: Timeline Infographic - A clear visual timeline showing the different methods of fetal heart rate detection (Transvaginal US, Doppler, Fetoscope) and the corresponding gestational ages (6 weeks, 10-12 weeks, 18-20 weeks). This helps students differentiate the methods and their timing.
Visual 2: Illustration - A simple diagram comparing the appearance of a transvaginal ultrasound probe, a handheld Doppler device, and a fetoscope to help students visually associate the tool with the method.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Timeline of Fetal Heart Rate Detection as background academic context rather than a clinical decision trigger.
Detecting the fetal heartbeat is a positive and reassuring sign of a viable pregnancy for both the healthcare provider and the expectant parents.
The normal fetal heart rate (FHR) range is 110 to 160 beats per minute (bpm). A rate consistently outside this range may indicate fetal distress and requires further investigation.
Auscultating the FHR helps differentiate it from the maternal pulse or other uterine sounds like the uterine souffle (a soft, blowing sound synchronous with the maternal pulse).

How to Approach the Question

First, identify the key components of the question: the method ('Doppler effect of ultrasound') and what is being detected ('foetal heart rate').
The question asks for the time when the FHR can be picked up, implying the earliest reliable point.
Recall the different methods for assessing the fetal heart during pregnancy and their specific timelines. Differentiate between visualizing cardiac activity on an ultrasound screen and audibly hearing the heartbeat.
Evaluate the options based on these milestones: 6 and 8 weeks are too early for an audible Doppler signal; this is the timeframe for visual confirmation on transvaginal ultrasound.
Consider the remaining options, 10 and 12 weeks. Both are within the correct timeframe. However, 10 weeks represents the beginning of the window when detection becomes possible, making it the best answer for when the FHR can be picked up.

Concept Tested & Keywords

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